US2663600A - Packed piston for high-pressure cylinders - Google Patents

Description

Patented Dec. 22, 1953 PACKED PISTON FOR'HIGH-PRES'SURE CYLINDERS Y Donald Harwood Newhall, Walpole, Mass.

Application December 29, 1950, Serial No. 203,299

The present invention relates to improvements 'in packed pistons for use in high pressure cylinders.

It is the principal object of the invention Vto p rcvide for use ina high pressure power cylinder a novel and improved packed piston assembly of the general type which comprises a lip type packing of a resilient material, a piston head on the end face of which the packing is supported and secured, and a backing-up element for the paci:- ing, these parts in accordance with the invention ,being constructed and arranged in a novel manner to support hydrostatic pressures far in excess of those previously considered practical for conventional cup or U-shaped packings, vand with improved wearing quality and long life for the packing.

' In carrying out the invention the lip-typepacking is' utilized'n combination with a backing-up ring which is of substantially triangular crosssection and rides against a beveled surface'forlned on the outer edge of the piston'iace so that the backing-up element will be forced outwardly 'against the cylinder wall as pressure is applied. t The backing-up element associated with the liptype packing is arranged to engage against the cylinder wall with a pressure'which is 'automatically adjusted in accordance with the pressure Vwithin the cylinder to maintain for any conceiv- `'able variation of applied pressure a perfectiit between the backing-up element and the cylinder wall.

'The invention will be more particularly described in connection with the accompanying drawing in which Fig. l is a sectional viewof a power cylinder and associated double acting packed piston illustrating in a preferred form the several features of the invention, and Fig. 2 is a sectional view taken on a line 2-2 of Fig, 1.

Referring to the drawing, V'a power vcylinderis Ydesignated at I having a port* I2 and a second admitting under pressure andv exhausting' the iluid pressure medium from the two ends'oi theV cylinder. A double'acting piston is provided comprising a piston head I6, and a connecting rod i8 which passes outwardly through an aperture, not shown, in one end of the cylinder. Two cupshaped packings 22 and 24, which may be conventional leather packings with metal retainers 26, 28, are rigidly secured to the opposite end faces of the piston head i6, being tightened together between a split thrust Washer 2l and a tightening nut 29 on the piston rod I8.

In accordance with the invention, the leather s claims. (c1. soc-.4)

packings 22, 24 are further supported along the point of contact between the piston and cylinder wall bymeans of two backing- up ring elements 30, 32, each of which is formed as a continuous unbroken band substantially triangular in cross'- section and having one face vthereof which bears against the piston wall, a second face which lies in a plane transverse to the cylinder providing a support for the respective packing, and the third face which is arranged to bear against a correspondingly beveled surface onthe outeredge of the piston. -The bevel surfaces at the two ends of the piston are indicated respectively at 34 and 36, are truste-conical in shape, and each has a 'slope of approximately 45 from the'plane of the *end face of the piston. It will be understood that this angle is adjustable to suit particular condi'- tions. Inthe illustrated embodiment of the invention, a iinite clearance is provided between the outer'surface of the piston and the cylinder, which may be in the order of .0l-inch to .(l2inch.

The ring backing-up elements 30, 32,' as clearly shown in the drawing, have a cross-'sectional area which is substantially equal to the arear ofthe cut-out edge portion of the cylinder. y When a fluid medium which may, for example,

' "be water or oil'is introduced into the cylinder r`and'of a material having a high degree ofielasvD014? 1100 ShOWIlY at Opposite ends OI altna'ely 'ticity-so that the pressure exerted upon the ring under high pressure, the lip of the packing 22fis forced outwardly against the wall of the cylinder to form a seal. The endwise thrustof the hydrostatic pressure tends to distort the 4packing-"so that it is pressed exactly to the shape vof the supporting seat and when the *pressure is in excess of the normally rated capacity of the packing, there is a tendency for the packing materialto be extruded through any cra-ck or crevice, however minute, which it may find between theseating end surface oi` the piston andthe cylinder wall!k The backing-up ring elements 3G, 32', ina-acordance'vvithv the present invention, are ,So shaped by the contacting portions of the packing will cause vthe associated`backing-up ring to vexpand 45 l ment of the invention, itis contemplated that the l cylinder wall and backing-up ring will be composed of complementary friction eliminating ma; terials. As shown, the backing-up rings are of brass, and are in contact with the cammed surface of a steel piston and with the internal surface of a steel wall cylinder.

In the operation of the device and assuming

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