US2866072A - Thermal blanket circulating and control means - Google Patents

Description

Dec. 23, 1958 E. M. SMITH 2,866,072

THERMAL BLANKETCIRCULATING AND CONTROL MEANS Filed .Jan. 9, 1957 2 Sheets-Sheet 1 INVENTOR. EDWARD M. SMITH Dec. 23, 1958 E. M. SMITH 2,866,072

THERMAL BLANKET cmcuuwmc AND CONTROL MEANS Filed Jan. 9, 1957 2 Sheets-Sheet 2 INVENTOR. EDWARD M. SMITH A Tram/5r V United States Patent THERMAL BLANKET CIRCULATING AND CONTROL MEANS Edward Malcolm Smith, Mansfield, Ohio, assignor to Jet-Heat, Inc., Englewood, N.-J'., a corporation of New York Application January 9, 1957, Serial No. 633,293

16 Claims. (Cl. 219-39) This invention relates to improved thermal blankets of the type wherein a heat transfer fluid is circulated therethrough, and, more particularly, to improved apparatus for circulating the fluid and automatically controlling the fluid temperature to control the temperature of the blanket as desired.

Among the many advantages of the improved circulating and control apparatus of the present invention are those resulting from the reduced size, weight, and expense of the fluid circulator and the highly effective control action of the temperature control apparatus. This improved circulator and control apparatus of the present invention is described herein as being used for keeping the user comfortably warm, and many advantages are provided in this use.

The improved temperature control apparatus is extremely effective in maintaining the desired temperature beneath the blanket adjacent to the users body. Manual adjustment may conveniently be made to set this temperature as desired. This improved apparatus continuously and automatically controls the temperature of the circulating fluid in response jointly to two important factors. It automatically responds to both of the following: (1) the amount of heat transfer from the fluid occurring in the blanket and (2) the ambient temperature of the air in the room. Furthermore, this improved control quickly responds in case the fluid begins to overheat and immediately shuts ofif the heater.

Electric blankets have not proven fully satisfactory in many cases because of the ever present hazard of fire and shock and because of the reluctance of many people to sleep under an electrical device. Many people who have tried to use electric blankets have found that their sleep is troubled by a hesitanc'y to move or roll about naturally for fear of damaging the live wires within the blanket.

Occasionally during use an electric blanket will become bunched or folded while still energized. This reduces the exposed area and causes the rolled up portions of the blanket seriously to overheat. To reduce this hazard efforts have been made to utilize a large number of thermostats widely dispersed throughout the blanket. The use of numerous thermostats makes the blanket heavy and unnaturally bulky as well as greatly increasing the number of electrical connections and raising the manufacturing cost. These scattered thermostats. in electric blankets often tend to be considerably delayed in response to localized overheating due to bunching. The blanket material itself insulates the thermostats so that they. cannot quickly sense a rise in temperature except when the hot spot happens to be adjacent to one of them. All of these problems are highly satisfactorily overcome by the present invention as will be explained in detail further below. I I

Another problem with electric blankets is the necessity for protecting the heating elements and electrical connectors in the blanket so that they are unaffected by dry-cleaning or washing. Waterproofing has added p 2,866,072 Patented Dec. 23, 1958 to the manufacturing cost and weight as particular care is required in treating the conductors and circuit elements.

Since the shortcomings of the electric blanket were not satisfactorily corrected, it has been suggested that a blanket be provided with means for circulating a temperature regulated fluid through appropriate passages or tubes therein. This prior liquid blanket overcame the various hazards and psychological barriers occurring in the use of the electric blankets and it lends itself readily to repeated washings and dry cleanings without any special precautions required. This prior blanket system is described and claimed in copending application Serial No. 309,416, filed beptember 13, I952, and assigned to the same assignee as the present application. The present invention is in the nature of a further improvement thereover.

Among the advantages of the present invention is the provision of motor and pump means for circulating liquid through the blanket which are quiet-running and vibration free as desired. This improved circulator is less expensive to manufacture than prior units and is more efficient and rugged in operation, having a high strength against being knocked out of adjustment by any rough usage.

Among the many advantages of the improved circulator and control apparatus of the present invention are those resulting from the fact that the temperature is controlled in response both to the ambient temperature in the room and in response to the temperature of the liquid returning from the blanket to the circulator. In efiect, this improved control provides a highly successful combination of measurements of heat transfer occurring in the blanket and of ambient conditions.

In order to maintain a comfortable temperature beneath a blanket adjacent to the users body throughout the night regardless of temperatures changes in the room, the improved apparatus of the present invention automatically varies the temperature of the circulating liquid. Thus, as the room becomes colder during the middle of the night the temperature of the liquid in the blanket is raised. This maintains a comfortable temperature beneath the blanket in spite of the colder conditions in the room.

When the room warms up, the temperature of the circulating fluid automatically is lowered to maintaina comfortable temperature beneath the blanket.

As will be understood in detail from the present specification, maintaining constant the temperature of the liquid returning to the circulator does not maintain a comfortable temperature beneath the blanket adjacent to the users body. As the temperature of the room falls, an increasing fraction of the available blanket heat is lost into the room as a result of convection, conduction and radiation losses from the blankets to the room. Much less of this blanket heat is then transferred down into the area beneath the blanket where it is useful. Also, as the room grows colder, more and more body heat is lost from the users head and from the hands and arms if they are exposed. As the room temperature rises, these effects are, of course, reversed.

As a result of all of these operative relationships, as explained in the specification, changes in the ambient temperature are a very important factor in obtaining proper temperature at the users body.

In the illustrative embodiment of the present invention a thermostat is advantageously arranged to have a predetermined indirect sensitivity to the temperature of the liquid returning from the blanket and has a predetermined direct sensitivity to the ambient conditions in the room and responds thereto. Advantageously, this thermostat quickly responds to any abnormal increases in the temperature of the liquid in the circulator, thus immediately shutting off the heater to prevent overheatmg.

Accordingly, it is among the objects of the present invention to provide a new and improved pump and heating unit and a sensitive and highly effective automatic control and combined overheating protector for a liquid thermal blanket. The illustrative embodiment of the present invention 1ncludes a unique arrangement wherein pump friction losses are so reduced that a low power electric motor is sufficient effectively to circulate the fluid through the blanket tubes. Advantageously, this improved circulator pump is practically vibration free.

It is still another object of the present invention to provide a fluid heating chamber that is inexpensive to manufacture.

It is still a further object of this invention to provide a unique heat sensing control arrangement which is responsive to ambient temperature and to the temperature of the liquid and of the storage tank and heater.

It is still another object of this invention to provide an easily assembled circulating pump unit which may be manufactured at a minimum of cost.

Although in the accompanying drawings a preferred embodiment of the present invention is shown and is described in detail in this specification, it is to be understood that this embodiment is not intended to be either exhaustive or limiting of the invention, but, on the contrary, is chosen for the purpose of illustrating the invention in order that others skilled in the art may so fully understand the invention, its principles and the application thereof, that they may embody it and adapt it in numerous forms, each as may be best suited to the requirements of its particular use.

In the drawings:

Figure l is a perspective view of a liquid thermal blanket cooperatively connected to the im r ved circulating and control apparatus of the present invention;

Figure 2 is a longi udinal sectional view of the improved circulating and control a paratus;

Figure 3 is a horizontal sectional view of the circulating unit shown in Fi ure 2, the view being taken genera long line 3-3 in Figure 2;

Figure 4 is a sectional end view of the circulating and control apparatus. the view being taken generally along the line 4-4- of Figure 2;

Figure 5 is a nlan view of the heat sensing c ntrol of the circul tor. t is view being taken along the line 5-5 in Figures 2 and 3;

Fi ure 6 is a schematic diagram of the electric circuit in the circulating and control apparatus of the present invention;

Figure 7 is a plan View of the thermostat portion of the c ntr l apparatus; illustrating an alternative embodiment; and

Figures 8 and 9 are section views of the thermostat shown in Figure 7, taken on the lines 8-8 and 9-9, res ectively, in Figure 7.

Referring to Figure 1. a thermal blanket 10 of the circulating heat transfer liquid type is shown in cooperative arrangement with the im roved circulating, heating, and automatic temperature control apparatus 12. The control apparatus 12 is provided with suitable means 11 for connection to a conventional electrical outlet 13. The blanket is connected to the improved apparatus 12 by means of a liquid return line 14 and a supply line 16.

The thermal blanket It) has a grid of heat exchange passages shown as being formed by a series of flexible small diameter tubes of a plastic material as described in the above copending application. A suitable heat transfer liquid is circulated through these tubes for warming (or if desired for cooling) e l The heat exchange passages include a pair of headers 18 and 20 at the foot of the blanket 10. A Se of h p tubes 22 are connected from one of the headers 18 which serves as the intake header to the other or outlet header 20. The liquid is pumped by the circulator apparatus 12 through the intake header 18 and its communicating heat exchange tubes 22 and circulated back to the outlet header Ztl. From the outlet header the liquid flows into the return line 14 and then back into the circulator 12.

In Figures 2, 3 and 4 are illustrated a preferred embodiment of the improved circulator of the present in vention. A protective casing 24 protects the operating portion of the circulator, heating and control apparatus 12. Appropriate openings in the casing 24 (as shown at the lower right in Figure 2) accommodate the entry of the supply and return lines 16 and 14, and means 96 are provided at the opposite end of the casing for air flow into the interior in order to sense the ambient temperature.

The liquid for the system is introduced into a tank or reservoir 26 through an opening 28 in its top surface 30. The side wall 32 and the top portion 3% of the tank are preferably formed as an integral piece, cast from a suitable metal of high heat conductivity and corrosion resistance, such as cast aluminum, for example. In order to warm the heat transfer liquid, a heating element 34 is advantageously cast in place integral with the side wall 32. A low power motor 36 of the shaded-pole type suitable for cooling by ambient air is mounted below the tank 26. The rotor 33 is of the squirrel cage type and is separated from the stator magnet structure 4t by a thin air gap. A winding 42 energizes the motor.

In order to seal the bottom of the reservoir 26, a housing 44 of non-magnetic material of relatively low electrical conductivity in the form of a cup is inserted into the air gap so as to surround the sides and bottom of the rotor 38. This seal cup may advantageously be formed of stainless steel. A pump housing 46 extends out from the top of the rotor seal cup and is preferably integral therewith. The pump housing 46 may be made of magnetic or non-magnetic material as desired, but a more rigid and economical structure is provided by manufacturing the pump housing and cup seal as one piece, in which case non-magnetic material would be used. A flange extends out from the top edge of the pump housing and is secured to the tank body 32 by suitable means such as the machine screws shown. To insure a tight fit, a gasket 48 is placed above this flange at the area of contact.

An annular partition 50 is placed between the reservoir 26 and the pump housing 46, being set into a shoulder recess 52. This partition 50 is provided with a pump intake opening 53 at its center, thereby permitting liquid to flow down from the reservoir 26 into a pump chamber 54. In order to prevent the liquid being drawn down through the intake 53 from swirling and developing a vortex which might cause air to be sucked into the pump chamber, a cylindrical anti-swirl screen 55 surrounds the pump intake. The partition 50 is firmly held in place by this anti-swirl screen which is set into a recess 56 in the top portion of the tank body 32 and presses down against the partition.

As shown most clearly in Figure 3, the pump chamber wall 46 is preferably circular. A tangential outlet 58 feeds out from the perimeter of the pump chamber 54 and is connected to the supply line 16.

An impeller 60 consisting of two L-shaped blades 62 is positioned in the pump chamber 54 between the rotor 38 and the partition 50. The blades 62 extend out into the upper portion of the chamber 54 near its perimeter, and are integrally secured to an impeller disk 64 which is provided with a central hole 66. The impeller disk is held down on top of the rotor by means of a flanged bearing bushing 68 which is press fitted down through the disk and down through the center of the rotor 38. A shoulder 70 formed by a small flange on the upper end of the bushing presses the disk 64 tightly into engagement mam with therefor 38. A fixed rotor mounting shaft 72' passes up through the bushing 68, providing a post about which the rotor 38 freely rotates. A thrust bearing shoulder 74 preferably is formed as an integral part of shaft 72, and is positioned between the lower end of the bushing 68 and the bottom of the rotor cup 44. To retain the rotatable bushing 68 on the post 72, a washer is held down against a shoulder on the post by a nut screwe onto the reduced upper end of the post.

To operate the circulator, a liquid of moderate to high specific heat and relatively low viscosity, such as water containing a quantity of a permanent anti-freeze such as ethylene glycol, is poured into the tank 26 through the opening 28 which is normally closed by a screw plug 78. The fluid flows from the tank, through the opening 53 and into the pump chamber 54. The impeller 68 forces the liquid out of the pump chamber through the tangential outlet 58. During operation, a small amount of fluid seeps down through the small clearance 82 between the rotor 38 and the close fitting wall of the rotor cup housing 44. The seepage path passes down the clearance space 82 and into the space between the rotor and the bottom of the cup 44. The pressure at the center of the pump chamber 54 is less than that near the perimeter. Due to this pressure differential, the seepage is forced up through the bushing 68 and around the rotor shaft 72, and back into the pump chamber 54, thus desirably lubricating this bushing which is adapted to be lubricated in this manner.

The movement of the seeping liquid around the rotor 38 and up along the rotor shaft 72 also advantageously creates a lifting and centering effect. As a result, the tendency for Wear on the bearing surfaces of the rotor shaft 72 and the bushing 68 is greatly reduced. The centering effect also reduces the vibration of the rotating rotor and impeller, thereby keeping the running noise to a minimum as well as increasing the efficiency of the circulator. The power to operate the electric driving motor is reduced from a typical figure of about 35 watts required by former circulator motors to about watts required by this embodiment. As a result, the problem of motor cooling is substantially eliminated, as the very small amount of input energy not utilized to drive the motor and pump readily dissipates to ambient through the casing 24. With circulation entirely shut oif and the motor operating continuously (without any input to the heater 34), tests have shown that the motor will not overheat.

In addition to the features already referred to, it will also be observed that the centrifugal circulator of the present invention has the advantage over a positive displacement pump that it is not adversely affected by any restrictions. thatmay occur in the circulation system; A positive displacement pump, by comparison, may develop abnormally high pressures in the system upon occurrence of a restriction and can be seriously overloaded or even stalled. Furthermore, the centrifugal pump is much less liable to develop vibration and noise which would require auxiliary damping.

The fluid is circulated through the blanket as described above in connection with Figure 1 and returns to the tank 26 through the return line 14. The return line is connected up into the bottom of the tank 26 by an inlet nipple '84 secured into the flange 47. Advantageously,

this return flow discharges'beneath the liquid level in the reservoir, thus providing an air seal and preventing entry or air into the return line. Moreover, this construction has the advantage that both the tangential outlet 58 and the inlet nipple 84 are located in'the integral pump housing 46 and flange 47, rather than in the tank body 32. This enables the tank body 32'to be formed in one piece with the heating element 34 of a castable material, which does not lend itself'readily to making tubing connections by soldering; bracing or the like. Thisalso eliminates the expense: of separately affixing heating means to the tank body 32 and provides better heat conductivity and control action and safety as explained below.

A temperature control 98 senses the ambient. temperature, and, indirectly, the average temperature of the fluid returning from the blanket and is ready immediately to respond to any tendency to overheat and thus shut off the heating element. In response to the ambient temperature, and in accordance with the heat transfer occurring in the blanket as measured by the average temperature of the liquid in the reservoir 26, the control regulates the temperature of the circulated liquid so as to keep the blanket user comfortable. In addition this control 90 shuts off the heating element if the tank body should become overheaded. A unique arrangement has been provided which accomplishes all of these functions and yet uses but a single thermostat.

As shown in Figures 2, 3, and 5, a thermostat 90 is positioned on a thermostat mounting plate 92 in a thermostat compartment 93. This mounting plate electrically insulates the thermostat control 90, and provides a predetermined amount of heat insulation between the thermostat and the circulator and reservoir. The mounting plate 92 is located within the circulator casing 24 and is. aflixed to the tank body 32 by means of a screw 95 or the like. The mounting plate is separated from the tank body 32 by a heat conduction metal backing plate 94. The thermostat 90 is attached to the lower end of the mounting plate 92 so as to be isolated from the tank body 32 and near the inflow of air through the port 96, to make it truly responsive to ambient air temperature. Air convection ports 96 in the casing side wall 97 permit the ambient air to circulate in the vicinity of the thermostat 96, as described more fully hereinafter. The heat conduction plate backing 94 carries a controlled portion of the heat from the tank body 32 to the areas adjacent to the thermostat 90.

In this way, the thermostat 90 is directly responsive to the temperature of the ambient air. It is also indirectly responsive to the average temperature of the liquid in the reservoir 26 as determined by the controlled amount of this heat which is conducted through the backing plate 94 and through the mounting plate 92. Thus, it can be seen that any desired balance can be achieved between ambient temperature effect and reservoir temperature effect. For most purposes, it is preferable to rely primarily on ambient temperature for control purposes and to sense reservoir temperature for protective purposes. If for any reason the heating element 34 tends to overheat, this heating is conducted through the heat conduction plate 94 to the thermostat. It will be appreciated that the position of the heat conduction plate closely adjacent to the bulge on the tank body containing the central part of the heating element renders the thermostat quickly responsive to overheating.

In order to obtain a desirable joint response to liquid temperature and ambient temperature a conduction plate 94 of metal of good heat conductivity such as aluminum or copper of an inch thick and an insulating plate of rigid insulating material /8 of an inch thick such as phenol formaldehyde (Bakelite) or methyl methacrylate (Lucite or Plexiglas) may be used.

The thermostat 90 may comprise a bimetal strip 98 which is attached at one end to the mounting plate 92. At this end, the strip 98 is in contact with a wiring terminal 99.

At its free end, the strip 98 carries a contact button 1%. which is engageable with a similar button 102 mounted on the plate 92 and included in the electric circuit described hereinafter. The fixed contact button 102 preferably is mounted on a small permanent magnet'elecut 104 which cooperates with the movable bimetal strip 98 to ensure positive action in opening and closing of the contacts. The fixed contact 102 is connected electrically to a wiring terminal 103.

Near its mounted end, the bimetal strip 98 carries an L-shaped lever member 105 which is engageable by a rotatable cam 106 above the strip 90 for adjusting the temperature at which the contacts 100, 102 will open and close. The cam 106 is carried at the lower end of an adjusting shaft 107 of electrical and thermal insulation material which is held rotatably in a half-round vertical groove in the mounting plate 92 by suitable means such as a spring clip 108. The shaft 107 extends upwardly through the casing 24. At its upper end outside the easing, the shaft carries a control knob 109 to permit ready adjustment of the thermostat. In the usual case, the control knob will be calibrated to reference indicia (not shown) on the top of the casing 24.

The thermostat 91B is connected in the electrical circuit of the control unit 12 as shown in Figure 6. In this circuit, the thermostat 91) is connected in series with the heater 34 across the motor winding 42. In this circuit, it will be observed that the bimetal strip 98 is shown as a resistance element. This strip preferably is made of a combination of relatively high resistance materials, such as chrome-nickel steels, so that current flow therethrough will result in some heating of the bimetal strip. This heating of the strip 98 serves two purposes. For one thing, it provides a small amount of heat in the thermostat compartment 93 which creates a chimney effect, inducing ambient air flow through the compartment 93. As the sensing element 98 is located in the lower part of the chamber 93, it is seen that this element will be exposed to fresh incoming ambient air, to be responsive thereto. The control circuit also preferably includes a manual on-olf switch 111 which may be located adjacent to the control knob 109 (Figure 2).

When the on-off switch 111 is closed, the motor 36 will operate continuously to maintain constant circulation of liquid through the blanket 10. When the unit is first turned on, it can be. assumed that the thermostat contacts 100, 102 will be closed so that electric current also will start to flow through the heater 34- and the thermostat 90. This will initiate heating of the liquid in the reservoir 26 and also will start heating the bimetal strip 98 to induce air circulation through the thermostat chamber 93.

Current flow through the heater 34 and the thermostat 90 will continue for a period of time determined by the temperature of the ambient air to which the strip 98 is exposed. Also, the temperature of the circulating liquid entering the reservoir 26 will influence the temperature of the chamber wall In turn, this will have a hearing on the temperature of the conducting plate 94 and of the lower portion of the mounting plate 92.

Thus, the bimetal strip will be exposed to three temperature efiects; one being due to current flow through the strip 98, another being the temperature of the ambient air entering the chamber 93, and the third being the return liquid temperature. After a period of current flow through the heater 34 and thermostat 90, the strip 98 will become heated sufficiently to open the thermostat contacts 1130, 102 and shut off the heating current.

After a short time, assuming no change in ambient temperature and assuming that the liquid temperature still is not up to the required level, the thermostat contacts will close again and flow of heating current will resume. This on-oii' cycling will continue as long as the unit continues in operation, with variations in cycle time as determined by ambient temperature and liquid temperature.

The current tiow through the bimetal strip 93, and the consequent heating effect thereof on the strip will be essentially constant. Therefore, the time required for the thermostat strip 98 to open the contacts 100, 10.; on each cycle will depend on the rate of heat loss from the strip. In turn, this will depend on the temperature difference between the ambient air and the strip 93, and also the temperature difference between the mounting plate 92 and the strip. An increase in either the ambient air temperature or the mounting plate temperature will reduce the heater on time and increase the heater off time, thereby reducing the average heat input to the circulating liquid to permit the temperature thereof to decrease. As far as the mounting plate temperature is concerned, it is seen that this arrangement provides an elfective safety control.

If, for example, circulation through the blanket is interrupted for some reason, the temperature of the reservoir wall 32 will go up rapidly. This temperature rise will quickly be transferred to the lower portion of the mounting plate 92 by the backing plate 94, causing the strip 9% to bend and hold the contacts 100, 102 open until the chamber wall 32 has cooled to a safe level.

In Figures 7-9 there is shown an alternative form of thermostat in the control unit of the present invention. In this embodiment, the thermostat comprises a main bimetal strip 98 mounted at one end on a spacer block 113 and attached by rivets 114 or the like to the mounting plate 92. The rivets 114 extend through the plate 92 to engage a wiring terminal 99 on the rear side of the plate 92. Also, the wiring terminal 103 for the fixed contact button 102 is located on the rear side of the plate 92.

In place of the backing plate 94 of Figures 2, 3 and 5, the control thermostat 90 in Figures 7-9 further includes a supplementary bimetal strip on the back side of the mounting plate 92. At one end, this supplementary bimetal strip 115 is attached to the mounting plate 92 by any suitable mounting means and so located as to engage the reservoir wall 32 when the mounting plate is in position. Accordingly, it is seen that the supplementary strip 115 is in direct thermal contact with the chamber wall 32 and will be directly responsive to the temperature thereof.

The supplementary strip 115 extends to a point adjacent to the main bimetal 98, and the free end of the strip 115 is engageable with one end of a reciprocable plunger 116 of insulating material. This plunger 116 extends through the mounting plate 92 so that its other end is engageable with the main bimetal 98 adjacent to the contact button 100. The plunger 116 is slidable endwise through the panel 92, so that it can be moved by the supplementary strip 115 into engagement with the main bimetal 98, upon flexing of the strip 115.

With this arrangement, it is preferable to have the control of circulating liquid temperature primarily dependent on the main bimetal 98, with the supplementary strip 115 being primarily operative as a safety control. In other words, the main bimetal 98 will cycle the heater on and off at a rate determined by the'ambient temperature, while the supplementary strip 115 will function at temperatures above the desired level to force the main strip into open contact position through the medium of the reciprocable plunger 116.

It will be understood, of course, that the desired operating temperature can be selected by rotating the knob 109, as previously described, that a change in the setting of the knob 109 will alter the temperature at which the main bimetal contacts 100, 102 will open and close. It will be observed that any change in the setting of the .control knob 109 will also change the temperature at which the supplementary strip 115 acts on the main bimetal 98 to open the contacts 100, 102.

With the arrangement shown in Figures 7-9, the effect of this is that when a lower liquid temperature is selected at the knob 109, the supplementary bimetal 115 becomes effective at a higher temperature than before, because of the greater curvature of the main bimetal 98. In many instances, it is preferable to have the response temperature of the supplementary strip 98 increase and decrease in step with increases and decreases in the temperature selected at the knob 109. This is accomplished very readily by reversing the relative locations of the plunger 116 and the contacts 100, 102. In other words, if the plunger 116 is so located as to contact the strip 98 at I or near the f ree end thereof, while the contacts 100, 102

are placed a slight distance inward from the free end of the strip, the response temperature of the supplementary strip will rise and fall as the temperature selected at the knob 109 is raised and lowered. This, of course, advantageously provides better protection against overheating, particularly when a relatively low liquid temperature is selected at the knob 109.

The circulator, heating and control apparatus is efiicient in operation requiring'only a ten watt motor and is very quiet. Typical overall dimensions of the casing 24 are 3 inches high, 5% inches long, and 3% inches wide.

From the foregoing it will be understood that the improved circulating, heating and control apparatus of the present invention described above is well suited to provide the advantages set forth. It will be understood that many changes and modifications may be made of the various features of this invention and the apparatus described herein may be varied in various parts, all Without departing from the true spirit and scope of the invention as covered in the following claims.

What is claimed is:

1. Improved circulating and heating apparatus for use with thermal blankets comprising a tank, heating means integral with said tank, a pump housing and impeller beneath said tank, said pump housing having an intake communicating with the interior of said tank through the lower portion of said tank, said pump housing having an outlet adapted to be coupled to a thermal blanket, and an electric motor drive means connected to said impeller.

2. Improved circulating and heating apparatus for use with thermal blankets comprising a tank, heating means integral with said tank, a pump housing and impeller beneath said tank, said pump housing forming at least a portion of the bottom of said tank and having an intake communicating with the interior of said tank, said pump housing having an outlet adapted to be coupled to a thermal blanket, an electric motor drive means connected to said impeller,

3. Improved circulating and heating apparatus for use with thermal blankets comprising a tank having top and side portions, a bottom for said tank including an impeller chamber integral therewith, said impeller chamber having an intake communicating with the liquid in the bottom of said tank, said impeller chamber having an outlet adapted to be coupled to a thermal blanket, an electric motor drive means connected to said impeller, and heating means for warming the liquid in said tank.

4. Improved circulating and heating apparatus for use with thermal blankets comprising a tank body, heating means for warming liquid in said tank, an integral member secured to said tank body and forming the bottom of said tank, said member having a cup therein extending downwardly and said member defining an impeller housing above said cup and beneath said tank, said impeller housing having an impeller therein and communicating with the interior of said tank at the bottom of said tank, said impeller housing having an outlet adapted to be coupled to a thermal blanket, and electric rotor drive means within said cup connected to said impeller.

5. Improved circulating and heating apparatus for use with thermal blankets comprising a tank having a body portion, an electrical resistance heating element integral with said body portion, an integral member sealing up the bottom of said tank, said member having a deep cylindrical cup therein and said member defining an impeller housing above said cup and beneath said tank body portion, said impeller housing communicating with the liquid in the lower portion of said tank body, an electric rotor within said cup, an impeller secured to said rotor and being positioned in said im eller housing beneath said tank body portion, an outlet from said impeller housing adapted to be secured to said blanket, and an electric motor magnet structure around s id cup.

6. Improved circulating and heating apparatus of the type: a. circulating liquid through a liquid thermal means whereby liquid flows from said tank down into said pump means by gravity flow, said pump means having an outletadapted to be coupled to a thermal blanket,

' and a liquid return from said thermal blanket entering said tank beneath the liquid level therein, thereby forming an air seal.

7. Improved circulating and heating apparatus of the type for circulating liquid through a liquid thermal blanket, said apparatus comprising a tank, heating means integral with said tank, a pump impeller beneath said tank, electric motor drive means including a rotor connected to said impeller, and a housing enclosing said impeller and the rotor of said electric motor, said housing eifectively scaling up a portion of the bottom of said tank.

8. Improved circulating and heating apparatus of the type for circulating liquid through a liquid thermal blanket, said apparatus comprising a tank, heating means integral with said tank, a pump impeller beneath said tank, electric motor drive means including a stator and a rotor connected to said impeller, and a housing enclosing said impeller and the rotor of said electric motor, said housing being placed in the air gap between the rotor and the stator of said electric motor.

9. Improved circulating and heating apparatus of the type for circulating liquid through a liquid thermal blanket, said apparatus comprising a tank, heating means arranged to warm liquid in said tank, a pump impeller of the centrifugal type beneath said tank, electric motor drive means including a rotor beneath said impeller connectedto' said impeller and a stator, a housing enclosing said impeller and the rotor of said electric motor, said I housing communicating with the interior of said tank through an impeller intake opening over the center of said impeller, a tangential outlet from said housing near the periphery of said impeller, and a vertical shaft within said housing extending up through the center of the rotor for mounting said rotor; the wall of said housing being in closely spaced relationship with said rotor and defining a small gap, whereby said impeller rotates as the rotor is rotated and seepage of some of the circulating liquid is forced downwardly between the housing wall and the rotor and upwardly about the shaft at the center of the rotor, creating an uplift effect upon said rotor.

10. Improved circulating heating and control apparatus of the type for circulating a heat transfer liquid through a thermal blanket, said apparatus controlling the temperature of the space beneath said blanket in accordance with changes in room temperature, said apparatus compri:ing a casing, a liquid reservoir tank within said casing and having a body portion of metal of good heat conductivity, a resistance heating element within the body of said tank, a pump and electric drive means within said casing, said pump having an intake communicating with said tank and an outlet adapted to be coupled to said blanket, a support of good heat conductivity secured to said tank body, a heat insulating mounting on said support, a thermostat on said mounting, and means defining an ambient air convection path through said casing, said thermostat being responsive to the air in said path and to the heat conducted through said support and mounting.

11. Improved circulating, heating and control apparatus as claimed in claim 10 and wherein said thermostat is secured to said support at a distance from the connection of said support to said tank body, andsaid thermostat is positioned in said air convection path near the point where the air enters said casing, thereby to sense ambient air temperature.

12. Improved circulating and heating apparatus for use with thermal blankets comprising a tank having a body portion with integral side and top walls, heating means integral with said side and top walls, an electric motor having a stator and a rotor, said rotor being beneath said tank, a cup-shaped liquid seal around said rotor within the gap between said rotor and stator, said seal defining an impeller housing above said rotor and having a flange secured to said side walls, said seal effectively forming the bottom of said tank, said impeller housing having an annular partition forming the top of said housing, said partition having a central opening communicating with said tank and forming the intake for said impeller housing, an impeller within said housing and aiiixed to said rotor, an outlet from saidhousing communicating with said blanket, a thermostat, a support of good heat conductivity being secured to said side and top walls of the tank body, said thermostat being secured to said support at a distance from said side and top Walls of the tank body, and heat insulating material between said thermostat and the support, thereby to predetermine the response of said thermostat to the temperature within said tank, said thermostat being exposed directly to the ambient air.

13. Improved circulating and heating apparatus as claimed in claim 12 and including liquid return discharge means adapted to be coupled to the return line from said blanket, said return discharge means being secured to said flange and discharging into the bottom of said tank, thereby to be beneath the liquid level in said tank.

14. Improved circulating and heating apparatus as claimed in claim 12 and wherein said tank includes a cylindrical anti-swirl screen therein, a recess in said top wall of the tank receiving the upper end of said screen, the lower end of said screen pressing down upon said portion around said pump intake opening.

15. Improved circulating and heating apparatus of the type for circulating heat transfer liquid through a liquid thermal blanket, said apparatus comprising: a casing, a liquid reservoir in said casing, means in said casing adapted to heat the liquid within said reservoir, means in said casing for circulating liquid through said reservoir, an electrical control circuit connected to said heating means,

a thermostat for said control circuit including a bimetal strip, a first fixed contact in said control circuit, a second movable contact in said control circuit carried by said bimetal strip and engageable with said first contact, said strip being movable upon heating thereof to open said contacts and de-energize said heating means, a second bimetal strip directly contacting a wall of said reservoir, and means coupling said strips and operable to move said first strip in a contact-opening direction upon heating of said second strip.

16. Improved circulating and heating apparatus of the type for circulating heat transfer liquid through a liquid thermal blanket, said apparatus comprising: a casing, a liquid reservoir in said casing, means in said casing adapted to heat the liquid within said reservoir, means in said casing for circulating liquid through said reservoir, an

electrical control circuit connected to said heating means, 1

a thermostat for said control circuit including a bimetal strip, a first fixed contact in said control circuit, a second movable contact in said control circuit carried by said bimetal strip and engageable with said first contact, said strip being movable upon heating thereof to open said contacts and de-energize said heating means, means defining an ambient air convection path through said casing, said bimetal strip being located in said air convection path, said bimetal strip being included in said electrical control circuit to constitute a portion of the path for current flow to said heating means, said bimetal strip comprising a combination of materials of relatively high electrical resistance whereby to provide heating of said strip in response to electric current flow therethrough, thereby to effect cyclical operation of said heating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,896,953 Hassell Feb. 7, 1933 2,312,353 Miller Mar. 2, 1943 2,319,730 Garraway May 18, 1943 2,753,435 Jepson July 3, 1956

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