US2779294A - High pressure pump - Google Patents

Description

HIGH PRESSURE PUMP William Reginald Dermot Manning, St. Alban, England Original application January 15, 1952, Serial No. 266,534. Divided and this application July 12, 1954, Serial No. 442,851

1 Claim. (Cl. 103-158) This invention relates to pumps or compressors capable of generating pressures greater than 1,000 atmospheres. This application is a division of my copending application Serial No. 266,534, filed January 15, 1952.

Such pumps or compressors are used in chemical processes where fluid materials are subjected to high pressures, such as, for example, in the polymerization of ethylene.

In pumps or compressors previously used for generating pressures of the order of 1,000 atmospheres, or more, it has been found that there is serious risk of failure by fatigue. Such failures have been found to occur at some irregularity of the section, such as the valve passages in the cylinder head, or in the attachment of the head to the parallel portion of the cylinder. The occurrence of a failure at such high pressures might well have serious consequences, and one expedient which has been used to avoid such an occurrence is the replacement of the cylinder head after a predetermined number of strokes.

It is the object of this invention to reduce this danger very greatly.

According to the present invention, We provide a twostage reciprocating pump or compressor capable of generating pressures greater than 1,000 atmospheres comprising a cylinder embodying two axially-aligned pump chambers of different diameters. A central wall integral with the cylinder separates the chambers and has a duct therethrough controlled by a non-return valve. A pair of spaced opposed stationary plunger-type pistons extends into the pump chambers from the opposite ends of the cylinder, and the latter is reciprocated to the pistons. A pump inlet duct and a pump outlet duct are provided in the larger and in the smaller pistons, respectively, and valves for the pump inlet and outlet ducts are located at the free or inner ends of the corresponding pistons.

If the available material is strong enough and the permissible dimensions are suiticient to contain the required pressure without producing stresses (as calculated by the Lam hypothesis) that exceed the fatigue limit, simple monobloc cylinders can be safely used. For higher pressures, it may be necessary to employ reinforcing means for both the central wall and the side walls of the chambers, such as making the cylinders in concentric parts and shrinking them together, or wire-winding a core tube. Care must be taken with both reinforcing methods, however, to avoid over-straining the material during construction. For the former, the most economical design procedure is described in Engineering, vol. 163, No. 4240, page 349, May 2, 1947, but care must be taken to see that the residual stresses are not too high and this can be done by using the method described in En gineering of December 8, 1950, in an article entitled Residual contact stresses in built-up cylinders.

One form of our invention is illustrated in the accompanying drawing which represents a mid-sectional elevation of a two-stage pump or compressor. The means for driving and supporting the pump are not shown. The reciprocating cylinder is built up from two axially nited States Patent 2,779,294 Patented Jan. 29, 1957 symmetrical concentric components 1 and 2, component 2 having been shrunk onto component 1. In this type of pump or compressor, a compound cylinder is preferred, in order to reduce tensile stresses about the oneway valve between the chambers, which is later described. The inner component 1 has two axially-aligned cylindrical chambers 9 and 10 separated by a central wall 11 and connected by a duct 12 controlled by a conventional non-return valve 7. Chamber 10 is of larger diameter than chamber 9. Preferably, the side surfaces of the chambers curve smoothly into the central wall surfaces to eliminate stress-concentrating abrupt angles.

A piston 4 is located in chamber 9, and a seal is provided by the gland 3. A second piston 6 is similarly located in chamber 10. The pistons 4 and 6 have central ducts 13 and 14, respectively, for conveying fluid and conventional non-return valves 5 and 8, respectively, at their inner ends. The two pistons 4 and 6 are fixed, and the cllinder is arranged to reciprocate relatively thereto.

-In operating the pump or compressor, when the cylinder moves from the right-hand end of its travel toward the left, valve 8 opens and fluid is drawn into chamber 10. At the same time, fluid present in chamber 9 is compressed and delivered through valve 5 into discharge duct 13. On the return stroke, as the cylinder moves to the right, fluid in chamber 16 passes through valve 7 into chamber 9. Since chamber 9 is smaller than chamber 10, this transfer will involve a rise in pressure of the fluid material.

The compression which takes place in chamber 9 will lead to a rise in temperature in this part of the pump,

and it is desirable that a suitable cooling means (not shown) be provided to prevent an excessive rise in temperature. This may take the form of a cooling jacket (not shown) surrounding the reciprocating cylinder and through which cold water is passed.

The stresses in the neighborhood of the valve seats and ducts cannot be calculated with any degree of certainty, but, since they are predominantly compressive, the risk of failure at these points owing to fatigue is very greatly reduced.

It is to be understood that the exact type of glands or valves used would be chosen according to the Working substance and the conditions of operation, e. g., pressure temperature, running speed. The requirements of the glands are just the same as those that would have to be met in a pump or compressor of conventional type.

I claim:

A two-stage reciprocating pump capable of generating pressures greater than 1,000 atmospheres comprising: a reciprocating cylinder of uniform exterior diameter having axially aligned bores of different diameters extending inwardly from the opposite ends of said cylinder and separated by a central wall continuous with the side walls of said bores, the interior junctions of said side and central Walls being curved to eliminate stress-concentrating abrupt angles; a one-piece reinforcing jacket coextensive with the length of said cylinder and shrunk thereonto; a duct in said central wall connecting said bores; a non-return valve controlling said duct; a pair of relatively-fixed plunger-type, stationary pistons mounted in said bores; a pump inlet duct in the larger of said pistons and a pump outlet duct in the smaller of said pistons; and one-way valves controlling said inlet and outlet ducts at the inner ends of said pistons.

Dow May 4, 1886 Jewell Apr. 25, 1922

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