US3893625A

US3893625A - Pumpless recirculating system for flowable materials

Info

Publication number: US3893625A
Application number: US484658A
Authority: US
Inventors: Richard F Wiggins
Original assignee: Gyromat Corp
Current assignee: Gyromat Corp
Priority date: 1974-07-01
Filing date: 1974-07-01
Publication date: 1975-07-08
Anticipated expiration: 1992-07-08
Also published as: CA1018859A

Abstract

Disclosed herein is an automatically controlled system, including a large constantly pressurized source tank, a small unpressurized collection tank, and an intermediate lock tank suitably interconnected therebetween for alternate, selective communication with said collection and source tanks for continuously supplying and recirculating a normally flowable, ''''non-pumpable'''' material to a series of spray guns and for replenishing the material, from time to time, as it is consumed in spraying processes.

Description

United States Patent Wiggins July 8, 1975 [54] PUMPLESS RECIRCULATING SYSTEM FOR 2,386,039 10/1345 Eatcan 3' 2 2,386,046 H) l 45 0! er 1 72 2,703,138 3/1955 Amon l37/575 X [75] inventor: Richard F. Wiggins, Fa rfi C n- 3,164,325 1/1965 Veum 239/126 3,246,845 4/1966 Techler et al... 239/7] [73] Ass'gnee- The Gymma 3.524.471 8/1970 Bresser 239/71 ux Stmford- Conn- 3,599,866 8/1971 Bolton 239/127 x [22] Filed: July 1, 1974 Primary ExaminerRobert S. Ward, Jr. [21] Appl' 484658 Attorney, Agent, or Firm-Mandeville and Schweitzer [52] US. Cl. 239/127; 239/7]; ll3377/557725; [57 ABSTRACT [51] Int Cl Bosh 9/0 Bosh 7/24 Fwd llloo Disclosed herein is an automatically controlled sys- [58] Field 259/71 73 2 124427 tem, including a large constantly pressurized source 239/148 569 137/263 tank, a small unpressurized collection tank, and an in- 400 termediate lock tank suitably interconnected therebetween for alternate, selective communication with said [56] Re'erences Cited collection and source tanks for continuously supplying and recirculating a normally flowable, non- UNITED STATES PATENTS pumpable material to a series of spray guns and for 3 2 325 Pegt replenishing the material, from time to time, as it is 2332" 3 l l As consumed in s ra in rocesses. 2,273,344 2/1942 Black et al... 239/126 p y g p 2,278,819 4/1942 Gredell 239/124 10 Claims, 2 Drawing Figures CLEANING .25 v}cso 151R 2 9 |4 L. E

PRESSURE swrrcu 1 100 B \Ol REGULATOR 91 H T 10 REPLENISH g'g v9 1 PUMPLESS RECIRCULATING SYSTEM FOR FLOWABLE MATERIALS BACKGROUND OF THE INVENTION In conventional recirculating systems for supplying spray guns or like devices, at least one and often several pumps are included in a coating material supply circuit for moving the spray medium to and/or from a supply tank or source. While these conventional systems have usually proved effective for handling conventional, pumpable spray media, certain coatings, which are desirably applicable by spray techniques, may be handled to much greater advantage without being subjected to mechanical pumping while certain other coatings are non-pumpable and may not be used at all in conventional systems. The non-pumpability of these spray media is typically occasioned by the deleterious effects of the pumping action on the physical properties of the spray material, itself, or conversely by the deleterious effects of the spray material on the pump apparatus.

Accordingly, when non-pumpable material is required to be sprayed, specially designed handling and recirculating systems must be provided. It is to a new and improved materials handling and continuously recirculating system for any flowable substances, and more particularly non-pumpable substances, e.g., water soluble resins, emulsions, and/or any flowable substances which tend to break down when subjected to the handling forces of mechanical pumps, that the present invention is specifically directed.

SUMMARY OF THE INVENTION In accordance with the present invention, a nonpumpable liquid spray medium may be continuously recirculated and supplied to a spray gun in a ciosed loop by employing a vertical stack of three tanks, the lowermost one of which is pneumatically pressurized and serves as a supply tank, the uppermost one of which is non-pressurized and serves as a recovery tank, and an intermediate one of which serves as a swing" or lock tank. The intermediate tank may be periodically pressurized and unpressurized to transfer, by gravity, spray medium from the upper to the lower tank, without process interruption. As an important aspect of the invention, automatic controls are provided to ensure that, during the changes of the lock tank pressurization from pressurized to unpressurized states, the spray medium is continuously supplied to the spray guns and circulated, at velocity sufficient to avoid settling of pigments or solids, in the loop from the lower tank to the upper tank under positive pressure.

Specifically, a typical recirculating system for a flowable spray medium embodying the inventive concepts includes a series of spray guns which are constantly fed from the source tank. As will be understood, the flowable, non-pumpable medium is forced under pneumatic pressure (air, nitrogen or other inert gas) from the source tank to the spray guns or spray devices where it may be sprayed, as required, onto an article, and the medium which is not sprayed from the gun or spray device is returned under pressure into the nonpressurized collection tank where it accumulates.

Advantageously, the pumpless system involves a series of three tanks, preferably arranged in vertically stacked relation. Return material flows through a failsafe valve and a flow regulator into the upper tank which is unpressurized. From time to time, the upper tank is drained through a solenoid controlled valve into the intermediate tank, when it is in an unpressurized state. Spray medium is forced through the circulating system from the lower or source tank, which is maintained under predetermined pressure at all times and without interruption during system operation. When the source tank becomes depleted, the intermediate or lock tank is pressurized to the same pressure as the lower tank through a solenoid controlled air valve, and the material stored in the lock tank is drained, by gravity, into the lower tank. The lock tank is then isolated from the lower tank, through the air valve, and depressurized, enabling it to receive more material from the collection tank. Replenishment of the continuously circulating material is made, automatically or manually, from time to time to compensate for the material used in the coating process.

DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and a better appreciation of its attendant advantages, reference should be made to the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a schematic representation of a pumpless recirculating system for a flowable, non-pumpable spray medium including stacked tanks embodying the inventive principles; and

FIG. 2 is a schematic wiring diagram for the automatic control of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, the pumpless recirculation system of the present invention is specially designed to handle and circulate sensitive coating materials such as emulsions, dispersions, water soluble resins and other water soluble coating or painting materials which are, or tend to be, deleteriously affected by the pumping action of mechanical pumps. That is to say, emulsions raise serious handling problems when used in conventional pumps, since the physical effects of the pumping action tend to cause foaming and/or otherwise to break down the emulsions rendering them unsuitable for application by the coating means.

Conventional recirculating coating systems generally include coating stations having a plurality of guns through which the paint or other coating medium is constantly recirculated under a pressure head generated by a conventional pump. In these conventional systems, the paint is constantly circulated in a closed ioop from the pump to the guns and back to the pump again, with paint being withdrawn from the loop by the periodic spraying of workpieces traveling through or past a coating station. Pumping systems such as these are not suitable for handling emulsions, dispersions, pump sensitive" and/or otherwise non-pumpable materials.

In accordance with the principles of the present invention, flowable, non-pumpable material is circulated in a closed loop from a large pressurized source tank 20 to and through multiple spray devices 22 and through supply lines 21 from the last of the devices 22 through a recirculating line 23 back into a small, unpressurized collection tank 24. The closed circulation loop is completed by an interposed lock tank 25, which may be selectively pressurized to the pressure of the source tank 20 or unpressurized to the atmospheric pressure of the collection tank 24, which communicates with the collection tank 24 through a lock tank supply line 26 and which communicates with the source tank 20 through a lock tank delivery line 27.

Advantageously and in accordance with the principles of the invention, the

tanks

20, 25, and 24 are vertically stacked and are supported on a common column 28, as shown in FIG. 1, with the unpressurized collection tank 24 in the uppermost position and the pressurized source tank in the lowermost position. As will be understood, this enables gravity feed to be employed between tanks 24 and 25 and, alternatively, between

tanks

25 and 20, when the pressurization of the communicating tank pairs are equalized. While the aforementioned gravity feed is a convenient and an economical mode of transferring coating materials consecutively from tanks 24, 25 and tank 20, in the closed loop, it will be understood that such transfer may be effected by suitably differentially pressurized tanks which need not be vertically stacked.

As an important aspect of the present invention, the source tank 20 and the lock tank 25 have

cover members

30, 31, respectively, which may be simply clamped or otherwise fastened to the

tanks

20, 25 to form pressure vessels. To simplify construction of an access to the

tanks

20, 25 for maintenance, the

cover members

30, 31 do not have any piping or other plumbing extending therethrough. The tank 24 may be closed by a cover to keep it clean and free of contaminants and to prevent evaporation, although it does not require a cover for its maintenance at atmospheric pressure in the illustrative embodiment described herein.

The source tank 20 is substantially larger than the collection and lock tanks 24, 25, respectively. For example, with a source tank having a capacity of approximately 50 gallons, each of the tanks 24, 25 require only a capacity of approximately 5 gallons for effective continuous recirculation. As a more specific aspect of the present invention, an automatic control system is provided which includes solenoid operated valves associated with the tanks. Control is derived through logic circuitry, liquid level probes located at predetermined elevations in each of the three tanks and appropriate relay devices. The coating material is kept constantly circulating in a closed loop, and the material is maintained in adequate supply by replenishing the source tank, from time to time, to compensate for the depletion of the coating material from the closed loop.

Specifically, the source tank is pneumatically pressurized through a source of air 9, which is supplied through a regulator 10, check valve 11, and shutoff valve 12, to the upper portions of the source tank through an air line 13. This pneumatic pressure, as will be understood, forces the coating material in the source tank 20 out through the supply line 21 to and through the spray devices 22 and back through return lines 23 towards the collection tank 24. The returning coating material passes through a solenoid operated, fail-safe valve 40 (open when energized) and a manual, velocity control valve 41 immediately upstream of the collection tank 24. Should the returning, collected coating material rise to an unsafe and dangerously high level, normally closed contacts 43, associated with a collection tank probe 42 located toward the top of the collection tank 24, will open upon contact of the liquid with the probe. This will deenergize a solenoid 44, controlling the valve 40, to close said fail-safe valve (FIG.

2). The flow control valve 41 may be manually adjusted to regulate flow of the coating material circulating through the closed, pumpless coating material loop. As shown, an overflow spout 45 is disposed at upper portions of the collection tank 24 to allow excess quantities of collected coating material to safely overflow into an overflow drum 46.

A solenoid-actuated, lock tank supply valve is interposed in lock tank supply line 26 and is normally maintained open by the energization of its control coil 57 through normally closed contacts 56 of a first latching relay 53. The relay 53 also includes normally open contacts 55, normally closed contacts 54, and normally open, time delay contacts 58.

As will be understood, latching relay 53 is a bistable device, which is normally non-energized, in which state its

contacts

54, 55, 56 and 58 are in the conditions mentioned. When energized, the aforementioned contact pairs reverse or flip-flop their normal conditions, when the relay is energized, i.e., if normally opened, they are closed, and vice versa. As shown in FIG. 2, the normally closed relay contacts 54 of the relay 53 are in series with the normally open contacts 51a associated with the upper probe 51 in the lock tank 25, which probe contacts are closed by the absence of liquid from probe 51. The normally open relay contacts 55 are in series with normally open contacts 524, associated with the lower probe 52 in the lock tank, which contacts similarly will be closed by the absence of liquid contact with the probe 52.

Thus, in the normal condition, latching relay 53 will be unenergized allowing its normally closed contacts 56 to energize coil 57 to hold valve 50 open. In accordance with the invention, coating material will be able to freely flow by gravity from tank 24 through supply line 26 and open valve 50 into the lock tank 25. When the level of coating material in the lcok tank 25 reaches the probe 51, normally open contacts 510 will be closed, thereby energizing the latch relay 53 and reversing the normal conditions of

contacts

54, 55, 56 and 58. With contacts 56 open, coil 57 will be deenergized, closing valve 50.

With time delay contacts 58 closed, after a momentary time delay sufficient to enable the latching of the relay S3 to become effective, coils 61 and 71 will be energized. These coils control a solenoid actuated threeway air valve in air line 14 and a two-way solenoid actuated source tank supply valve in line 27, to open, respectively, valves 60 and 70 shortly after valve 50 closes.

in accordance with the invention, the pneumatic pressure of

tanks

25 and 20 will be equalized by the communication of the tanks through the valve 60 and

air lines

13, 14, permitting coating material to flow through the liquid line 27 and valve 70 into the source tank'by gravity. Thereafter, when the pressurized lock tank 25 drains to below the level of the lower probe 52, the normally open contacts 520 associated with the lower probe will be closed by the absence of fluid contact with the probe, the closure of which contact will momentarily reenergize latching relay 53 through contacts 55 (which were closed during the reversal of the contact positions during the previous energization of the latching relay). With the reenergization of the latching relay, its

associated contacts

54, 55, 56 and 58 are reset to their norrnal conditions indicated in FIG.

2, for the subsequent repetition of the above-described cycle.

With the opening of contacts 58, the coils 61, 71 will be deenergized causing valve 70 to close and allowing valve 60 to be returned to a position of venting tank 25 to atmosphere. In addition, valve 50 will be reopened through the reenergization of the coil 57 through the once again closed contacts 56, to allow collected coating material to flow from collection tank 24 by gravity into tank 25.

As a more specific aspect of the invention, a provision for automatic pressure relief is included in the system to limit the pneumatic pressure in the source tank during filling with liquid. To that end, a pressure switch 100, having normally open contacts 103 associated therewith, is disposed in air line 13. The contacts 103 are set to close when the pressure in the tank exceeds, by approximately two or three pounds, the predetermined operating tank pressure, as established by the regulator 10. Thus, when the pressure in tank 20 rises above the two or three pounds tolerance, contacts I03 associated with pressure switch 100 will be closed energizing coil 102, which controls solenoid valve 101, to hold valve 101 open until the pressure in the line 13 is reduced sufficiently to reopen the contacts 103. In practice, the pressure relief valve 101 will tend to open and to close repeatedly during the filling of source tank 20.

Replenishing of the supply of non-pumpable coating material continuously recirculating in the closed loop may be accomplished either manually or automatically. To the end of automatic replenishment from a pressurized coating supply 90 through filling line 91, the logic circuitry (FIG. 2) of the invention further includes a second latching relay 80 having two sets of normally open contacts 84, 85 and a set of normally closed contacts 83. As shown in FIG. 1, the source tank 20 is provided with a high level probe 82 having associated therewith normally opened contacts 82a, which will be closed when contacted by liquid, and a low level probe 81 having associated therewith normally opened contacts 81a, which will be closed by the absence of liquid contact therewith. The contacts 820 are in series with the normally open latch relay contacts 84 while the contacts 81a are in series with the normally closed latch relay contacts 83. Thus, when the liquid level in the source tank 20 falls beneath probe 81, contacts 81a will close, thereby momentarily energizing latching relay 80 through its normally closed contact 83, thereby reversing the condition of

contacts

83, 84, and 85. The paint supply 90 will be actuated and operated through the closure of latching relay contacts 85 to fill the source tank 20 through the supply line 90 until the liquid level reaches probe 82. At this time, probe contacts 820 will close thereby reenergizing the latching relay 80 to reset it by reversing the condition of

contacts

83, 84, 85, thereby halting operation of the paint supply 90. lt will be understood that the paint supply 90 may be in the form of a pressurized tank similar in construction and operation to that of the lock tank for the purposes of introducing paint into the pressurized source tank. Alternatively, paint may be added to the system through the unpressurized collection tank 24.

As shown in FIG. 2, indicator lights 120, 121 and 122 may advantageously be included in association with the

coils

44, 102 and 61, 71, respectively, for the purposes of providing visual indications of system conditions at any given moment.

For cleaning the tanks of the system, manual override switches 110, Ill, and 112 are included in the control circuitry to energize directly the

coils

61, 71, and 102. This will open the valves 50, 60, and for the purposes of flushing a cleaning solution through the stacked tanks and out through a cleaning discharge line 113 at the bottom of the source tank 20, which line 113 includes a manual valve 114.

lt should be understood that the specific form of the invention herein illustrated and described is intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. For example, the lock tank 25 may be pressurized independently of the source tank 20 to a substantially higher pressure, from an independently, automatically regulated air (gas) supply 9' (shown in phantom), in order to transfer coating material at a vastly accelerated rate in comparison with the rate realized from gravity alone.

I claim:

1. A closed loop system for continuously circulating non-pumpable coating medium to a spray device, including a. inlet line means for supplying said spray device;

b. return line means for recirculating non-sprayed medium supplied to said spray device;

c. a non-pressurized collection tank in communication with and receiving the coating material exiting from said return line means;

d. a lock tank disposed beneath said collection tank and being normally maintained at atmospheric pressure while being selectively pressurizable at predetermined times to predetermined higher pressure;

. lock tank supply line means communicating between said collection tank and said lock tank and having a selectively actuatable lock tank supply valve included therein;

f. a pressurized source tank for supplying a coating material under pressure to said inlet line;

source tank supply line means extending from the bottom of said lock tank to said source tank and having a source tank supply valve included therein;

. first air line means for pressurizing said source tank and the coating medium therein communicating between said source tank and a supply of gas under pressure;

. second air line means communicating between said lock tank and said source of gas under pressure;

j. air line valve means selectively actuatable either to interconnect said first and second air line means or to isolate said first air line means from said second air line means while venting said lock tank to atmospheric pressure;

. control means for said supply valves and said selectively actuatable air line valve means to normally maintain said source supply valve closed, said lock tank supply valve opened, and said lock tank vented to the atmosphere through said selectively actuatable air line valve;

. whereby said non-pumpable coating material normally flows from said collection tank to said lock tank by gravity while said coating material is forced through the remainder of said recirculating closed loop under air pressure;

m. whereby, from time to time, said lock tank supply valve may be closed and said source tank valve may be opened and said air line valve means may be actuated selectively to interconnect said first and second air line means to equalize the pressure in said lock tank and said source tank to accommodate the flow of non-pumpable coating material from said lock tank to said source tank under gravity.

2. The system of claim I, which further includes a. a solenoid actuated fail-safe valve along with a flow control valve in said return line means.

3. The system of claim 1, in which a. said lock tank control valve is controllable in response to the liquid level in said lock tank.

4. The system of claim 1, in which a. said first air supply line means includes a pressure sensor and a pressure relief valve which are adapted to cooperate to relieve excessive pressures generated in said source tank.

5. The system of claim 1, in which a. said lock tank being selectively pressurizable, from time to time, to a predetermined pressure greater than the pressure in said source tank.

6. The system of claim 1, in which a. said source tank and said lock tank are in the form of pressure vessels having plumbing-free cover means.

7. The system of claim I, in which said system further includes non-pumpable coating medium to a spray device, including a. inlet line means for supplying said spray device;

e. lock tank supply line means communicating between said collection tank and said lock tank and having a selectively actuatable lock tank supply valve included therein;

g. source tank supply line means extending from the bottom of said lock tank to said source tank and having a source tank supply valve included therein;

h. first air line means for pressurizing said source tank and the coating medium therein comm unicat ing between said source tank and a first supply of gas under pressure;

. second air line means communicating between said lock tank and a second supply of gas under pressure for pressurizing said lock tank to a pressure greater than that of said source tank;

j. air line valve means selectively actuatable either to interconnect said lock tank and said second supply of gas or to isolate said second supply of gas from said lock tank while venting said lock tank to atmospheric pressure;

k. control means for said supply valves and said selectively actuatable air line valve means to normally maintain said source supply valve closed, said lock tank supply valve opened, and said lock tank vented to the atmosphere through said selectively actuatable air line valves;

. whereby said non-pumpable coating material normally flows from said collection tank to said lock tank by gravity while said coating material is forced through the remainder of said recirculating closed loop under gas pressure;

m. whereby, from time to time, said lock tank supply valve may be closed and said source tank valve may be opened and said air line valve means may be actuated selectively to interconnect said second air line means to pressurize said lock tank to force the non-pumpable coating material from said lock tank to said source tank under pressure.

I t i

Claims

1. A closed loop system for continuously circulating nonpumpable coating medium to a spray device, including a. inlet line means for supplying said spray device; b. return line means for recirculating non-sprayed medium supplied to said spray device; c. a non-pressurized collection tank in communication with and receiving the coating material exiting from said return line means; d. a lock tank disposed beneath said collection tank and being normally maintained at atmospheric pressure while being selectively pressurizable at predetermined times to predetermined higher pressure; e. lock tank supply line means communicating between said collection tank and said lock tank and having a selectively actuatable lock tank supply valve included therein; f. a pressurized source tank for supplying a coating material under pressure to said inlet line; g. source tank supply line means extending from the bottom of said lock tank to said source tank and having a source tank supply valve included therein; h. first air line means for pressurizing said source tank and the coating medium therein communicating between said source tank and a supply of gas under pressure; i. second air line means communicating between said lock tank and said source of gas under pressure; j. air line valve means selectively actuatable either to interconnect said first and second air line means or to isolate said first air line means from said second air line means while venting said lock tank to atmospheric pressure; k. control means for said supply valves and said selectively actuatable air line valve means to normally maintain said source supply valve closed, said lock tank supply valve opened, and said lock tank vented to the atmosphere through said selectively actuatable air line valve; l. whereby said non-pumpable coating material normally flows from said collection tank to said lock tank by gravity while said coating material is forced through the remainder of said recirculating closed loop under air pressure; m. whereby, from time to time, said lock tank supply valve may be closed and said source tank valve may be opened and said air line valve means may be actuated selectively to interconnect said first and second air line means to equalize the pressure in said lock tank and said source tank to accommodate the flow of non-pumpable coating material from said lock tank to said source tank under gravity.

2. The system of claim 1, which further includes a. a solenoid actuated fail-safe valve along with a flow control valve in said return line means.

7. The system of claim 1, in which said system further includes a. high and low liquid level indicators in said source tank; b. control means associated with said high and low liquid indicators to replenish said paint supply in said source tank to said high level whenever said paint supply falls below said low level probe.

8. The system of claim 1, in which a. said collection tank, lock tank, and source tank are vertically stacked.

9. The system of claim 8, in which a. the collection tank, lock tank, and source tank are supported on a common vertical column means.

10. A closed loop system for continuously circulating non-pumpable coating medium to a spray device, including a. inlet line means for supplying said spray device; b. return line means for recirculating non-sprayed medium supplied to said spray device; c. a non-pressurized collection tank in communication with and receiving the coating material exiting from said return line means; d. a lock tank disposed beneath said collection tank and being normally maintained at atmospheric prEssure while being selectively pressurizable at predetermined times to predetermined higher pressure; e. lock tank supply line means communicating between said collection tank and said lock tank and having a selectively actuatable lock tank supply valve included therein; f. a pressurized source tank for supplying a coating material under pressure to said inlet line; g. source tank supply line means extending from the bottom of said lock tank to said source tank and having a source tank supply valve included therein; h. first air line means for pressurizing said source tank and the coating medium therein communicating between said source tank and a first supply of gas under pressure; i. second air line means communicating between said lock tank and a second supply of gas under pressure for pressurizing said lock tank to a pressure greater than that of said source tank; j. air line valve means selectively actuatable either to interconnect said lock tank and said second supply of gas or to isolate said second supply of gas from said lock tank while venting said lock tank to atmospheric pressure; k. control means for said supply valves and said selectively actuatable air line valve means to normally maintain said source supply valve closed, said lock tank supply valve opened, and said lock tank vented to the atmosphere through said selectively actuatable air line valves; l. whereby said non-pumpable coating material normally flows from said collection tank to said lock tank by gravity while said coating material is forced through the remainder of said recirculating closed loop under gas pressure; m. whereby, from time to time, said lock tank supply valve may be closed and said source tank valve may be opened and said air line valve means may be actuated selectively to interconnect said second air line means to pressurize said lock tank to force the non-pumpable coating material from said lock tank to said source tank under pressure.