US3626474A

US3626474A - Pressure indicator and bypass pressure relief valve

Info

Publication number: US3626474A
Authority: US
Inventors: Kurt F Hammer
Original assignee: Purolator Inc
Current assignee: Purolator Courier Corp
Priority date: 1969-11-13
Filing date: 1969-11-13
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07

Abstract

An indicator and bypass pressure relief device for use in a system having a high-pressure side and a low-pressure side, which indicates or signals an increase of pressure in the high-pressure side of the system beyond a predetermined differential limit; and bypasses fluid from the high-pressure side to the low-pressure side of the system to relieve such high pressure whenever it exceeds a predetermined differential pressure limit.

Description

United States Patent lnventor Kurt F. Hammer Carnarillo, Calif.

Appl. No. 876,374

Filed Nov. 13, 1969 Patented Dec. 7, 1971 Assignee Purolator, Inc.

Rahway, N.Y.

PRESSURE INDICATOR AND BYPASS PRESSURE RELIEF VALVE [56] References Cited UNITED STATES PATENTS 2,998,138 8/1961 Mould et al 210/90 3,128,743 4/1964 210/90 X 3,150,633 9/1964 210/90 X 3,364,897 1/1968 210/90 X 3,371,787 3/1968 210/90 3,420,266 1/1969 137/553 Primary Examiner-Henry T. Klinksiek Attorney-Wham & McManigai ABSTRACT: An indicator and bypass pressure relief device for use in a system having a high-pressure side and a low-pressure side. which indicates or signals an increase of pressure in the high-pressure side of the system beyond a predetermined differential limit; and bypasses fluid from the high-pressure side to the low-pressure side of the system to relieve such high pressure whenever it exceeds a predetermined differential pressure limit.

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r e 4 a5 5 5-36 e75 52 r 64 A "44 PRESSURE INDICATOR. AND BYPASS PRESSURE RELIEF VALVE BACKGROUND OF THE INVENTION My invention is useful in different arts but has a special utility in fluid or hydraulic systems or lubrication circulating systems such as employ a filter for filtering the fluid. When a filter starts to clog there is a gradual increase in back pressure on the high-pressure side of the system; and when this back pressure produces a predetermined differential in pressure between the high-pressure side and the low-pressure side of the system the filter must be replaced.

Also, an increase of pressure in the high-pressure side of such a system may occur due to pressure surges of different durations which would also cause the differential pressure between the high and low sides to increase above a predetermined limit.

Prior to my invention there were devices on the market for indicating such increases in differential pressure and such surges in high pressure, one such device being disclosed in the US. Pat. to Mouwen, No. 3,364,897, granted Jan. 23, I968.

Clogging of the filter or' high-pressure surges may cause such an increase in pressure on the high-pressure side of the system that damage may result. Present prior art devices known to applicant do not solve this problem and there is,

therefore, a need in these arts for a device which will visually or audibly indicate an increase in differential pressure whenever it exceeds a predetermined limit and which also will automatically bypass and relievethe pressure in the high-pressure side whenever such high-pressure exceeds a predetermined limit which might cause damage.

SUMMARY OF INVENTION My invention provides a device which is connected on one side to the high-pressure side of such a system, and on the other side to the low-pressure side of such system, and which functions to give an indication whenever the pressure differential between the high-pressure side and the low-pressure side exceeds a predetermined limit, and which further functions to bypass fluid from the high-pressure side to the lowpressure side in order to relieve high pressure whenever the differential in pressure exceeds a second predetermined limit. It is an object of my invention to provide a pressure indicator and bypass pressure relief device in which a movable pressure responsivemeans subjected to high pressure on one side and low pressure on the other side, functions to control the operation of differential pressure indicator means and also to control a bypass pressure relief means depending upon the magnitude of the pressure differential. I

It is another object of my invention to provide a device of the character described in which the pressure-responsive means is in the form of a piston which moves in response to differential pressures and which causes the operation of the indicator means and the bypass pressure relief means.

It is a still further object of my invention to provide a device of the character referred to in which there is an indicatoroperating means for operating the indicating means, which indicator-operating means is carried by the pressure responsive means but is not exposed to the high pressure side of the system in which the device is incorporated, and in which the indicator-operating means is movable relative to the pressureresponsive means. It is also an object of my invention to provide a pressure indicator and bypass relief device in which the indicator-operating means is carried by the pressure-responsive means and is directly exposed to the high pressure on the high-pressure side of the pressure-responsive means.

It is another object of my invention to provide a device of this character in which small valve leakages from the highpressure side to the low-pressure side of the system will not cause malfunctioning. It is a further object of my invention to provide a device of the character described in which an increase in pressure on the high-pressure side moves the pressure-responsive means into an indicator actuating position and in which a further increase in high-pressure moves the pressure-responsive means into bypass pressure relief position.

It is a still further object of my invention to provide a device of the character referred to in which the indicator means and the indicator operating means each have associated magnets with similar poles on adjacent sides whereby the movement of the indicator-actuating means into a position near said indicator means will cause movement of said indicator means into an indicating position as the result of the repelling action of the magnets.

Another object of the invention 'is to provide a fluid or hydraulic system having a low-pressure side and a high-pressure side with the means connected between the high-pressure side and the low-pressure side for indicating increases in differential pressures and for causing bypassing of fluid from the BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings, FIG. 1 is a diagrammatic view illustrating a portion of a system incorporating the features of my invention;

FIG. 2 is a longitudinal sectional view through a pressure indicator and bypass v pressure relief device incorporating the features of my invention, this figure illustrating the position of the parts in a normal nonindicating and nonbypassing position;

FIG. 3 is a view similar to FIG. Zbut showing the position of the .parts when the pressure in the-.highpressure side of the system has risen to a pressure difl'erential limit where an indication of such condition should be made;

FIG. 4 is a view similar to FIG. 2 but showing the position of the parts in bypass pressure relief position;

FIG. 5 is a cross-sectional view taken on the line 5-5 of FIG. 2;

FIG. 6 is a longitudinal sectional view through a second device incorporating the features ofmy invention, the parts in this position being in normal nonindicating and nonbypassing position; v

FIG. 7 is a view similar to FIG. 6 but showing the parts in a position in which the indicator means has been actuated to indicate that a certain predetermined pressure differential limit has been reached;

FIG. 8 is a longitudinal sectional view showing the parts in bypassing position; and

FIG. 9 is a sectional view taken on the line 9-9 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. I, the numeral 11 represents a conduit in the high-pressure side of a fluid system and the numeral 12 represents a conduit in the low-pressure side. Numeral 14 represents a filter device through which fluid is passed in order that a filtering action may be performed on it. In the course of the operation of the system the filter becomes spent and will gradually build up a back pressure so that the differential between the high pressure side and the low-pressure side will be increased.

My invention is not limited to a system in which a filter is an indispensible unit, the filter being representative of any type of ,fluid component in which a pressure drop may exist or be "lief device of my invention is indicated by the numeral 15 and is connected to the high-pressure side of the system' by'suitable piping or conduit 16 and to the lower side by suitable piping or conduit 17. Thus, it will be seen that the device is in parallel with the filter 14.

Referring now to FIGS. 2 to 5, the details of construction and operation of this form if my invention will be described.

The body is supported in a suitable housing 21, which is connected to the conduit 16 at 22 and to the conduit 17 for 23.

Suitable seals

24 and 25 are provided to form a leakage proofspace 16 in the housing 21.

The body 20 has a dividing wall 27 which divides the body into a pressure responsive means chamber or piston chamber 28 and an indicator element chamber 29. The cylindrical wall 30 forming the chamber or cylinder 28 has an upper bleed 31, a lower bleed 32, and a central bypass passage or passages 33, the bleed 32 and the bypass passages 33 being pressure drop ports whereby the pressure within the lower part of the chamber 28 during certain operation may be held above the low-pressure side of the system.

Within the chamber or cylinder is a differential pressureresponsive means or differential pressure piston or sensor piston 35 which has a cylindrical portion 36 which has sliding engagement with the cylindrical wall of the piston chamber. The piston 35 is biased in a downward direction or toward seat 37 by means ofa compression spring 38, one end of which engages the wall 27 and the other end of which engages the shoulder at the upper end of the cylindrical portion 36. Piston 35 has a diametrical wall 39 from which there extends a cylindrical flange 40, which provides an annular valve edge 41 which, in FIG. 2, is in engagement with the conical valve seat 37.

The valve seat 37 is provided by the upper end ofa seat element 43, which is held in place by rolling or crimping inwardly a flange 44 formed at the lower end of the body 20. The seat element has a central pressure passage 45 which receives fluid under pressure from the conduit 16 of FIG. 1. When the piston 35 is in the position shown in FIG. 2 with the valve edge 41 in engagement with the seat 37, area a of the lower end of the piston is exposed to high pressure fluid and tends to move the piston in a direction opposite to the force applied to it by the biasing spring 38.

Above the diametrical wall 39 is a chamber 47 having a bleed 48, which chamber slidably supports the indicator-actuating means of my invention which is provided in the form of a magnet 49 stepped at 50 so that the crimped upper end 51 holds the larger diameter portion of the magnet 49 in the chamber 47, the magnet 49 normally being held in extended position by a compression spring 53 in the chamber 47. The crimped lip 51 acts as a stop, as shown in FIG. 2.

The indicator element of my invention, generally designated by the numeral 55, has a body 56 supported within the chamber 29, the upper end of the chamber 29 being closed by an iron cap 57 held in place by a crimped lip 54. The recess 58 receives a magnet 59. It will be noted that the

magnets

49 and 59 have like poles on adjacent sides so that when the magnets are brought into adjacency there is a repelling action. The indicator element has a cylindrical indicator portion 60, which projects through a central cylindrical opening in the iron end plate 57. There is a compression spring 61 which normally holds the indicator element 55 in its retracted position as shown in FIG. 2 with the north pole of the magnet 59 in contact with an iron plate 63 mounted in a recess formed in the dividing wall 27. The pressure of the spring 61 plus the magnetic pull of the magnet on the iron plate 63 holds the indicator element 55 in the position shown in FIG. 2. Other than the magnets. the iron cap 57 and the iron disk 63, various parts of my invention, at least in the adjacency of the magnets, are made of nonmagnetic material.

As previously pointed out, the parts are shown in FIG. 2 in the positions which they occupy when there are no unusual pressure differential conditions between the high-pressure side and the low-pressure side of the system. At this time the pressure in the high-pressure side presses against the area a of the piston 35 exerting a force in a direction tending to move the piston 35 from the seat 37. At this time, however, there is the pressure of the low pressure side of the system plus the force of the biasing spring 38 tending to hold the piston 35 in seated position. The strength of the biasing spring 38 is such that its force in combination with the force applied by the lowpressure fluid will hold the piston seated during all normal and usual operations of the system. Should there by any leakage past the valve 41 the .bleed 32 connected to the space 64 prevents fluid from building up a pressure against the end face 65 of the piston 33, thus, inadvertently or improperly unseating this piston At this time the indicator element 55 is in retracted nonindicating position, being held in this position by the force of the spring 61 and the magnetic pull of the magnet as previously explained.

Whenever an increase in pressure occurs in the high-pressure side of the system, or whenever the differential in pressure between the high-pressure side and the low-pressure side of the system becomes sufficiently large that the force tending to unseat the piston 35 is greater than the force tending to seat the piston 35, the piston will then move away from the seat 37. This may occur by a pressure surge occurring in the system or may occur by the filter 14 of other element building up a back pressure such, for example, as would occur if the filter 14 becomes clogged over a period of use.

When this increase in pressure occurs the parts will ultimately move into the position shown in FIG. 3. This action occurs as follows: The first movement of the piston cracks the valve and high pressure now acts on the full piston area b "as indicated in FIG. 2. This produces a sudden increase in force which, in turn, causes the piston to rapidly travel in a direction away from the seat 37 until the spring 38 has been sufficiently compressed to again create a condition of equilibrium between the spring force and the fluid pressure. This position is shown in FIG. 3. The design of the device is such that this condition will occurjust before the lower edge 65 of the piston 35 leaves the corner 66 of the lower wall or walls of the bypass passage or passages 33. At this time the main flow through the bypass passages 33 is closed and the only flow taking place is that which goes through the bleed port 32 and any annular clearance between the piston 35 and the bore of the cylinder or chamber 28. This flow rate is predetermined by design requirements for the device and is a very small volume.

When the piston 35 moves into the position shown in FIG. 3, the north pole of the magnet 49 contacts the bottom face of the wall 27, and the repellent action resulting from like poles being brought adjacent to each other, produces a repelling force which causes the indicator 55 to move upwardly to that the body 56 engages the lower face of the iron plate 57, the south pole of the magnet being attracted to the iron body, thus holding the indicator element in this indication position wherein the cylindrical part 60 projects from the device and indicates that there has been an increase in pressure in the high-pressure side of the system or that a differential in pressure has reached a predetermined limit. Should the piston 35 during this operation over travel the position shown in FIG. 3, the spring 53 will yield, permitting relative axial movement between the piston and the indicator actuator element or magnet 49.

If the pressure increase in the high-pressure side of the system is merely a surge in pressure and the pressure after the surge returns to normal limits, the piston will again return to the position shown in FIG. 2 and operations will continue until a further increase may occur. However, the indicator 55 will remain in its indicating position thus telling an attendant that there has been an exceeding of the predetermined differential pressure limit and that an investigation of its cause should be made.

If the differential pressure increases above the pressure differential limit required to bring the parts into the position shown in FIG. 3 and cause the actuation of the indicator, the pressure differential or high pressure will be reaching an area beyond which damage might occur. When this first differential pressure is exceeded the piston 35 will then move into a position as shown in FIG. 4 to uncover the bypass passages or ports 33 so that fluid will be bypassed from the high-pressure side to the lowpressure side flowing through the conduit 16, the device and the conduit 17. The size of the bypass passages 33 is designed so that there will be a pressure drop across them in order to maintain the high pressure necessary to keep the piston in bypassing position during the time this high pressure continues. When the piston 35 moves from the position shown in FIG. 3 into the position shown in FIG. 4, there will be a relative telescoping movement between the magnet 49 and the piston 35 whereby the magnets rest almost entirely within the chamber 47. During this movement fluid must be expelled from the chamber 47 and this fluid will flow through the bleed port 48.

Again, if the high pressure which has caused the parts to move into the position shown in FIG. 4 is a temporary surge in pressure, the parts will, upon reduction in the pressure surge, return either to the position shown in FIG. 3 or to the position shown in FIG. 2, except 55 remains in extended position until manually reset, depending upon the amount of reduction in pressure.

The form of my invention shown in FIGS. 6 to 9 difiers in certain respects from the form just described. Generally the inventions are the same, but the form now under consideration differs from the first described form in that the indicator actuating means in directly exposed to the pressure on the high-pressure side of the system. Because of the similarity of many parts the same numerals will be used. Also because of similarity of functions, it will be unnecessary to describe all the functions nor will it be necessary to go into all the functions nor will it be necessary to go into all the details of construction as was done in connection with FIGS. 2 to 5. Where parts perform a similar function but are different in form or details of construction, the part number given to that part will be followed by the suffix a. For example the form in FIGS 6 to 9 has a piston which is of different form than the form in FIGS. 2 to 5 and, therefore, this piston will be given the identification 35a."

Referring to FIG. 6, this view shows the parts in the positions they occupy when the system is within normal pressure differential values. As in the first form, there is a body supported in a housing 21, the body 20 having a piston chamber or cylinder 28 which is connected to the low-pressure side of the system through a bleed passage 31 at its upper part and through'bypass passages or ports positioned closely adjacent to the valve seat and, therefore, will be identified as bypass passages or ports 33a.

The body 20 is provided with a seat element 43a which is threadedly connected to the lower end of the body by a threaded joint I00 and this seat element carries the lower 0- ring seal 25. The piston 35a is slidable in the chamber 28 and has a tapered valve face 41a which engages the knife edge seat 370.

In the piston 35a is an opening generally designated by the numeral 101 which extends axially from one end to the other end of piston 35a. The upper portion of this opening is in the form ofa cylinder 102, the central portion is in the form of an enlarged chamber 103, and the lower portion is in the form of a passage 104 which is separated from the chamber I03 by a conical seat 105. Positioned within and supported by the body 35a is an indicator actuator piston 490 which has a cylindrical body 107 recessed at its upper end to receive the magnet 108. The body 107 is slidable in the bore or cylinder I02 and the lower end of this body projects into the chamber 103 and has an O-ring seal I09 supported in a groove. The relative diameters of the body 107 and the cylinder I02 are such as to permit slight leakage However, when the indicator actuating means 49a is raised into a position as shown in FIG. 2, in which the seal 109 is within the bore 102, there is no leakage.

The lower end of the body is of reduced diameter as at 110, and provides a knife edge annular corner III which engages the seat 105. The indicator actuator is normally held against its seat by a biasing spring I12 and when the parts are in the position shown in FIG. 6 the area of the piston 49a exposed to the high-pressure side of the system is indicated at a. The area of the piston 35a, exposed to the high-pressure side of the system, is indicated by 0" which is the diameter of the knife edge seat 37a.

Under normal pressure conditions, the parts are as shown in FIG. 6, with both valve faces against their seats and the indicator 55 in a retracted position. At this time the pressure differentials are such as to be lower than valve cracking" pressure.

Differential pressure against the lower end of the indicator actuator element 49a is on the area a" and the high pressure against this area is opposed by the pressure on the low pressure side of the piston plus the spring force I12. If at this time there is a leakage past the seat III it is bled through the clearance between the cylinder I02 and the cylindrical body 107. This leakage, of course, is very small and is not considered measurable by normal means. The purpose of this bleed between 102 and 107 is to prevent pressure buildup which would act on the area b" which would result in actuation at a lower pressure than the predetermined differential pressure required to move the element 49a from its seat. The total exposed area of the piston 35a is as indicated at 0" and the pressure attempting to lift this piston from its seat prior to the actuation of the indicator actuating means 49a is an area equal to area c" minus area a. The load or force in a direction tending to move this piston 35a from its seat is balanced by force from the spring 38 plus, of course, the low pressure against the low-pressure side of the piston 35a, this combined force being adequate to hold valve 350 closed at all difi'erential pressures below the predetermined pressure differential at which the indicator is to be actuated.

As the differential pressure reaches the predetermined actuation pressure the pressure acting on area a overcomes the force tending to hold the indicator actuator against its seat and this means 49a will move away from the seat I05. When this movement occurs the pressure in the high pressure side of the system then acts on the larger area b" and the indicator actuator 49a rapidly moves away from the seat until the magnet 108 comes against the wall 27 and into a position as shown in FIG. 7. At this time the indicator 55 moves into an extended or actuating position as explained in connection with the first form of my invention.

After the parts have moved into the position shown in FIG. 7 the area of the piston 35a exposed to the differential position will be an area equal to c" minus It is to this area that the spring 38 is designed to function, and the piston 35a is held against its seat until such time as a higher predetermined differential pressure is reached, at which time the piston 35a will be moved from its seat. The large area"d" will now be exposed to high pressure, and the valve 35a will rapidly move into the position shown in FIG. 8. Fluid will now bypass through the pressure drop bypass passages 33a as shown in FIG. 8.

If thereafter the high pressure is reduced, the piston 35a may return to its seat as in FIG. 2 and if the pressure differential reduces further and to a normal range, the parts may ultimately return to the position shown in FIG. 6. As in the first form, however, the indicator 55 remains in indicating position in order that the attendant may know that there has been an increase in pressure and that an investigation should be made to determine its cause and whether or not the filter 14 should be replaced.

Iclaim:

l. A pressure indicator and bypass pressure relief device for use in a system having a high-pressure side and a low-pressure side, the combination including:

a. a movable piston exposed on one side to high pressure and on the other side to low pressure said piston being movable whenever differential pressure exceeds a predetermined minimum;

b. means for indicating a predetermined increase in differential pressure between the high pressure side and the low-pressure side of the system;

0. means for operating said indicator means carried by said piston and exposed directly to high pressure on the highpressure side of said piston, said indicator operating means being movable independent of said piston to actuate said indicator means upon a predetermined increase in differential pressure; and

d. means interconnecting said high-pressure side of said piston with the low-pressure side of the system for relieving pressure on said high-pressure side of said piston when the differential between high pressure and low pressure exceeds a second predetermined limit, said means being in cooperative communication with and operable by said movable piston.

2. A pressure indicator and bypass pressure relief device for use in a system having a high-pressure side and a low-pressure side, the combination including:

a. a movable piston exposed on one side to high pressure and on the other side to low pressure, said piston being movable whenever differential pressure exceeds a predetermined minimum;

b. means for indicating a predetermined increase in differential pressure between the high-pressure side and the low-pressure side of the system;

c. means for operating said indicator means, said means comprising a movable differential pressure-responsive element carried in said piston and having a portion exposed directly to the high pressure on the high-pressure side of said piston; and

3. A pressure indicator and bypass and a pressure relief device, the combination including:

a. a body having a chamber which has a high-pressure inlet and a low-pressure outlet;

b. pressure responsive means in said chamber exposed to high pressure on one side and low pressure on the other side;

c. means for indicating an increase in differential pressure between said high-pressure side and said low-pressure side;

d. means for operating said indicator means movably carried by said pressure-responsive means, said indicatoroperating means being movable by an increase in pressure on said high-pressure side of said pressure-responsive means into a position to actuate said indicator means; and

e. means interconnecting the high-pressure side and the low-pressure side of said pressure-responsive means for relieving high pressure on said high-pressure side. said means being operable by said pressure-responsive means as a result of a further increase in pressure on said highpressure side of said pressure-responsive means over and above that necessary to move said indicator-operating means into position to actuate said indicator means.

4. A combination as defined in claim 3 in which a first increase in differential pressure will cause movement of said pressure-responsive means to move said indicator-operating means into a position to actuate said indicator means and in which a higher differential pressure will move said pressure responsive means into bypass pressure relief position to open a bypass and relieve the pressure on said high-pressure side.

5. A combination as defined in claim 3 in which said indicator means indicates high-pressure surges on said high-pressure side without the opening of said high-pressure relief means.

6. A pressure indicator and bypass and a pressure relief device, the combination including:

a. a body having a chamber which has a high-pressure inlet and a low-pressure outlet; b. a cylinder in said chamber exposed to high pressure on one side and low pressure on the other side said cylinder having:

1. a seat at the high-pressure side of said cylinder;

2. a bleed means adjacent said seat and in communication with a low-pressure zone in said chamber in said body; and

3. a high-pressure relief port means in said cylinder communicating with a low-pressure zone in said chamber said relief port being spaced a further distance from said seat then said bleed means;

c. a piston means movable in said cylinder, said piston being adapted to sealably engage said seat in said cylinder and to operate said high-pressure relief port means as the result of an increase in differential pressure between said high pressure and said low-pressure side of said cylinder;

d. means for indicating an increase in differential pressure between said high-pressure side and said low-pressure side; and

e. means for operating said indicator means carried by said piston, said indicator operating means being movable by an increase in pressure on said high-pressure side of said cylinder into a position to actuate said indicator means.

Claims

1. A pressure indicator and bypass pressure relief device for use in a system having a high-pressure side and a low-pressure side, the combination including: a. a movable piston exposed on one side to high pressure and on the other side to low pressure, said piston being movable whenever differential pressure exceeds a predetermined minimum; b. means for indicating a predetermined increase in differential pressure between the high pressure side and the low-pressure side of the system; c. means for operating said indicator means carried by said piston and exposed directly to high pressure on the highpressure side of said piston, said indicator operating means being movable independent of said piston to actuate said indicator means upon a predetermined increase in differential pressure; and d. means interconnecting said high-pressure side of said piston with the low-pressure side of the system for relieving pressure on said high-pressure side of said piston when the differential between high pressure and low pressure exceeds a second predetermined limit, said means being in cooperative communication with and operable by said movable piston.

2. A pressure indicator and bypass pressure relief device for use in a system having a high-pressure side and a low-pressure side, the combination including: a. a movable piston exposed on one side to high pressure and on the other side to low pressure, said piston being movable whenever differential pressure exceeds a predetermined minimum; b. means for indicating a predetermined increase in differential pressure between the high-pressure side and the low-pressure side of the system; c. means for operating said indicator means, said means comprising a movable differential pressure-responsive element carried in said piston and having a portion exposed directly to the high pressure on the high-pressure side of said piston; and d. means interconnecting said high-pressure side of said piston with the low-pressure side of the system for relieving pressure on said high-pressure side of said piston when the differential between high pressure and low pressure exceeds a second predetermined limit, said means being in cooperative communication with and operable by said movable piston.

3. A pressure indicator and bypass and a pressure relief device, the combination including: a. a body having a chamber which has a high-pressure inlet and a low-pressure outlet; b. pressure responsive means in said chamber exposed to high pressure on one side and low pressure on the other side; c. means for indicating an increase in differential pressure between said high-pressure side and said low-pressure side; d. means for operating said indicator means movably carried by said pressure-responsive means, said indicator-operating means being movable by an increase in pressure on said high-pressure side of said pressure-responsive means into a position to actuate said indicator means; and e. means interconnecting the high-pressure side and the low-pressure side of said pressure-responsive means for relieving high pressure on said high-pressure side, said means being operable by said pressure-responsive means as a result of a further increase in pressure on said high-pressure side of said pressure-responsive means over and above that necessary to move said indicator-operating means into position to actuate said indicator means.

3. a high-pressure relief port means in said cylinder communicating with a low-pressure zone in said chamber, said relief port being spaced a further distance from said seat then said bleed means; c. a piston means movable in said cylinder, said piston being adapted to sealably engage said seat in said cylinder and to operate said high-pressure relief port means as the result of an increase in differential pressure between said high pressure and said low-pressure side of said cylinder; d. means for indicating an increase in differential pressure between said high-pressure side and said low-pressure side; and e. means for operating said indicator means carried by said piston, said indicator operating means being movable by an increase in pressure on said high-pressure side of said cylinder into a position to actuate said indicator means.

6. A pressure indicator and bypass and a pressure relief device, the combination including: a. a body having a chamber which has a high-pressure inlet and a low-pressure outlet; b. a cylinder in said chamber exposed to high pressure on one side and low pressure on the other side, said cylinder having: