US2828760A - Automatic cut-outs for hydraulic circuits - Google Patents

Description

A ril 1, 1958 F. D. TAYLOR ETAL AUTOMATIC CUT-OUTS FOR HYDRAULIC CIRCUITS Filed May 18, 1954 Zd J Iv o 15 1 United States Patent 9 AUTOMATIC CUT-CUTS FOR HYDRAULIC CIRCUITS Frank Desmond Taylor and John Linnell Fyleman, Gloucester, England, assignors to British Messier Limited, Gloucester, England, a British company Application May 18, 1954, Serial No. 430,712

Claims priority, application Great Britain May 19, 1953 5 Claims. (Cl. 137-115) The present invention comprises improvements in or relating to automatic cut-outs for hydraulic circuits.

In hydraulic circuits an automatic oflT-loading valve, or cut-out, is normally employed in conjunction with a hydraulic pump and there is usually also an accumulator to store part of the pump delivery. It is desirable to reduce the possibility of pressure differences arising between the two units as far as possible.

According to the present invention an hydraulic system having a pump, a cut-out for the pump and an accumulator is characterised by the fact that the accumulator and cutout are combined into one unit, the cut-out being located within an end fitting for closing the accumulator, so that there is no appreciable pressure difference between the accumulator and the pressure which operates the cut-out.

The following is a description by way of example of one construction according to the invention:

The accompanying drawing is a section through a combined accumulator and cut-out in accordance with the present invention:

An accumulator chamber 11 is provided of cylindrical shape, hemispherical at one end and open at the other. The open end is screw threaded externally and is closed by a fitting 12 screwed on to it which contains an automatic cut-out. This accumulator is of the usual type containing a floating piston 13 to separate air at the hemispherical end from hydraulic fluid. The hemispherical end is provided with an air filling valve 14.

The cut-out fitting has an inlet port 15 at the bottom leading to a non-return lift valve 16 and thence into the accumulator chamber 11. From the chamber there is an outlet port 18 to whatever hydraulic circuit there may be which is to be supplied.

Between the inlet port and the non-return valve there is a branch 21 leading to a pilot conduit 17.

The pilot conduit 17 opens at one end into the accumulator chamber and at the other end is connected to a port connected to exhaust (tank). A two-way pilot valve 23 extends through the conduit 17 having a head 22 at one end to seat on the opening to the accumulator and another head 19 at the other end to seat on a port 26 connected to the exhaust port 20. Beyond the head 19 is a spring 24 to keep the port 26 normally closed, and the port to the accumulator normally open. The spring is held up to the valve by an adjusting screw 25. The centre part 36 of the pilot valve is large enough nearly to fill the pilot conduit 17.

In the branch 21 which leads to the pilot conduit 17 there is a cylindrical by-pass chamber 27 having a seating 28 leading to the exhaust port 20. A main by-pass valve 29 has a cylindrical body which fits the chamber 27 and a reduced conical portion at the end to close the seating 28. The branch 21 from the normal fiow conduit enters this chamber below the cylindrical body of the valve 29 and above the seating 28 so that the pressure tends to lift the by-pass valve 29. The valve is made hollow and has a bleed hole 39 in the side which passes pressure fluid to the interior and then on to the pilot conduit 17; A light spring 31 urgesthe by-pass valve to closed position.

In operation, the pump delivers through the non-return valve 16 to the accumulator and builds up pressure therein. Pressure has access to the pilot valve both on the head 22 in the accumulator and through the bleed hole 30.- As this pressure will fill the by-pass chamber above the by pass valve 29, it holds the latter closed. When the pressure becomes suflicient to overconie the pilot valve spring 24, it moves the pilot valve 23 to open the exhaust port 26. Due to the double-headed construction of this valve and to the restricted passage for fluid between the centre part 36 of the pilot valve and the pilot conduit, the pilot valve tends to flick over rapidly from the first (or upper) position to the second (or lower). This opens the upper part of the by-pass chamber 27, above the by-pass valve 29, to exhaust and the pressure in the annulus of the bypass valve below the cylindrical body, lifts it and opens the by-pass exhaust port.

As soon as pressure falls to a point where the pilot valve spring 24 can close the pilot valve 23, the parts return to their first position.

The setting of the cut-out pressure, as mentioned before, is obtained by varying the load on the two-way pilot valve spring 24, and the ratio of cut-out to cut-in pressure is a function of the ratio of the valve seat areas of the top and bottom valve- heads 22 and 19 on the pilot-valve 23 and of the spring rate of the pilot valve spring 24.

We claim:

1. A combined hydraulic cut-out and accumulator unit comprising a vessel containing an accumulator chamber, an end fitting therefor having a main inlet supply passage to the chamber, a non-return valve in said passage, a bypass passage from the inlet passage on the outer side of said non-return valve leading to an outlet port, a by-pass valve in said by-pass, a piston operatively connected to said by-pass valve to actuate it, said piston being always open on one face to the inlet pressure and on the other face to pressure in a pilot passage extending from the interior of the accumulator to the outlet, a two-way pilot valve to control the pressure in the pilot passage, said pilot valve in one position closing the pilot passage to the accumulator and in another position closing it to its outlet, yielding means for urging the pilot valve to its second said position, a pilot-conduit from the inlet passage upstream of the non-return valve to the pilot-passage, and a main outlet supply passage from the accumulator chamber separate from the inlet passage.

2. A combined hydraulic cut-out and accumulator unit as claimed in claim 1, wherein the pilot valve is an integral one-piece double-headed poppet-type valve having one head outside the pilot passage facing toward the accumulator chamber and the other head facing toward the outlet and the yielding means bears on said second-mentioned head.

3. A unit as claimed in claim 1, wherein the yielding means to maintain the two-way valve in the position in which the bypass is connected to accumulatorpressure comprises a spring and means for adjusting the spring to vary the pressure cut-out limit.

4. A unit as claimed in claim 1, wherein the pilot conduit is connected to the outer delivery on the pump side of the non-return valve by a bleed-hole which permits flow through the by-pass valve piston.

5. A combined hydraulic cut-out and accumulator comprising a vesselcontaining an' accumulator chamber, an end fitting therefore having a main inlet supply passage to the chamber, a non-return valve in said passage, a bypass passage from the inlet passage upstream of the non-return valve and leading to an exhaust port, a bypass valve in said bypass passage, a pilot passage extending 2,828,760 p p A a from the interior of the accumulator chamber to exhaust, a two-way pilot valve member for the pilot passage and having at its opposite ends a pair of integral poppet-type valve heads, said pilot valve in one position closing with one of its heads communication between the pilot passage and the accumulator chamber and in a second position closing with its other head communication of the pilot passage with exhaust, spring means for urging the pilot valve to said second position, means for varying the spring pressure at will, a piston operatively-connected to the bypass valve to actuate it, said piston being always open on one face to the inlet passage pressure upstream of the nonreturn valve and on the other face to the pressure in 4 the pilot passage and having a bleed passage extending through it, and a main outlet supply passage from the accumulator chamber separate from the inlet passage.

References Cited in the file of this patent UNITED STATES PATENTS 2,401,845 Stephens June 11, 1946 2,473,953 Huber et al. June 21, 1949 2,545,712 Stevenson Mar. 20, 1951 2,621,598 Jerome Dec. 16, 1952 2,673,527 Ashton et al Mar. 30, 1954 2,696,828 Husing Dec. 14, 1954

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