JP4413019B2 - Fluid pressure detector - Google Patents

Description

  The present invention relates to a fluid pressure detection device that is provided in, for example, a lubrication system such as a machine tool or an industrial machine and detects the pressure of a fluid in a fluid supply line through which lubricating oil or the like flows. The present invention relates to a fluid pressure detection device that detects and detects pressure.

  In general, for example, in a lubrication system such as a machine tool or an industrial machine, there is a system that intermittently supplies lubricating oil such as grease or oil. The fluid supply line of such a lubrication system is used to detect abnormalities in which the lubricating oil is not normally supplied because the lubricating oil is clogged in the fluid supplying line or the lubricating oil leaks out from the fluid supplying line. A fluid pressure detecting device for detecting the pressure of the lubricating oil is provided.

Conventionally, this type of fluid pressure detection device is described in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 9-243485), and detects the pressure by detecting fluid compression enclosed inside.
As shown in FIG. 7, the fluid pressure detection device Sa includes a thick outer tube 1 and a thin flexible inner tube 2 attached to the radially inner side of the outer tube 1. An annular pressure receiving fluid enclosing portion 3 is formed between the outer tube 1 and the outer tube 1, and a pressure gauge 4 is connected to the pressure receiving fluid enclosing portion 3.

  When this fluid pressure detection device Sa is used, the fluid supply conduit is connected to the inner tube 2 so that the inner tube 2 of the fluid pressure detection device Sa forms part of the fluid supply conduit. When the lubricating oil flows from the fluid supply pipe to the inner pipe 2, the inner pipe 2 is bent by the pressure of the lubricating oil, and the bending pressure of the inner pipe 2 generates a compression pressure in the pressure receiving fluid of the pressure receiving fluid sealing portion 3. The pressure gauge 4 detects the compression of the pressure-receiving fluid, and the pressure of the lubricating oil flowing through the fluid supply line is detected.

Japanese Patent Laid-Open No. 9-243485

  By the way, in this conventional fluid pressure detecting device, since the pressure receiving fluid is sealed in the pressure receiving fluid enclosing portion 3, when a gas such as air is used as the pressure receiving fluid, the pressure receiving fluid expands due to a temperature change. If the expansion or contraction of the fluid supply line increases during the idle period when the lubricant does not flow in the fluid supply line, the starting point of the pressure value will be greatly different. There was a problem that there were things that could not be done.

  The present invention has been made in view of the above-described problems, and even when air expands or contracts due to a temperature change, the pressure of the fluid flowing through the fluid supply line can be detected without error. An object is to provide a detection device.

  In order to achieve such an object, the fluid pressure detection device of the present invention has a first cylinder having one end connected to a fluid supply conduit through which a fluid flows and a second cylinder communicating with the other end of the first cylinder. A cylinder body, a first piston that is inserted into the first cylinder so as to be movable back and forth, and a piston body that is provided integrally with the first piston and has a second piston that is inserted into the second cylinder. In the fluid pressure detecting device for detecting the pressure of the fluid in the fluid supply line by detecting the air compression in the second cylinder chamber, which is changed by the advancement of the piston body, the second cylinder chamber is opened to the atmosphere when the piston body is retracted. An open air route is provided.

When the fluid does not flow to the fluid supply conduit, no pressure is generated in the fluid in the fluid supply conduit, so the piston body is in the retracted state on the first cylinder side.
In this state, since the second cylinder chamber is opened to the atmosphere by the atmosphere release path, even if there is a temperature change in the second cylinder chamber and the air expands or contracts, the air enters and exits from the atmosphere release path. No pressure change in the cylinder chamber.
When the fluid flows into the fluid supply line, pressure is generated in the fluid in the fluid supply line, the fluid flows into the first cylinder chamber, the piston body enters the advanced state, and the air in the second cylinder chamber becomes the second. It is compressed by the piston, and this air compression is detected. At this time, since the second cylinder chamber is opened to the atmosphere by the atmosphere release path when the fluid is not flowing, there is no change in the starting point of the pressure value, and therefore, the piston body may be affected by the temperature change even in the advanced state. Since there is no pressure, the pressure is detected accurately.

Further, if necessary, the first cylinder is provided with a first seal portion that seals the inner surface of the first cylinder and the outer surface of the first piston, and the second piston advances into the second cylinder. A second seal portion that seals the outer surface of the second piston at a time while forming a gap with the second piston when the second piston is retracted, and the cylinder body includes the second piston and the second piston. An open hole that communicates with the gap between the two seal portions is formed, and the atmosphere release path includes the gap and the open hole.
When the piston main body advances, the second piston seals the second piston, so that the air is sealed in the second cylinder chamber and air compression is performed in the second cylinder chamber. The second cylinder chamber is opened to the atmosphere by an atmosphere release path communicating with the gap. Therefore, since the second seal portion is used for opening and closing the second cylinder, the structure can be simplified and the atmosphere can be easily released.

Furthermore, if necessary, a clearance is provided between the second piston and the inner surface of the second cylinder closer to the first cylinder than the second seal portion, and the open hole communicates with the clearance.
Since the open hole and the gap are communicated with each other via the clearance, the communication can be facilitated as compared with the case where the open hole and the gap are directly communicated.

  Furthermore, if necessary, the first cylinder is connected to a small-diameter portion formed on one end of the first cylinder on which the first piston slides, and a first step portion on the other end of the first cylinder. A large-diameter portion that is formed in communication with the small-diameter portion and into which the first piston and the second piston are loosely inserted, the first seal portion is formed in the small-diameter portion, and the second cylinder is One cylinder has a smaller diameter than the large diameter portion and communicates with the large diameter portion via a second step portion. The first piston is formed with a collar portion that stops against the first step portion when the piston is retracted. A coil spring for urging the piston body toward the first cylinder is provided between the second step portion and the flange portion.

  When no fluid flows through the fluid supply pipe, the piston body is forcibly moved to the first cylinder side by the coil spring. For this reason, the second cylinder chamber is quickly opened to the atmosphere by the atmosphere release path, and the starting point state can be reliably ensured.

Further, if necessary, the first seal portion is provided with a V packing provided on the small diameter portion of the first cylinder, and a C-shaped ring provided on the second cylinder side of the V packing and fitted to the small diameter portion. And a ring presser provided on the second cylinder side of the ring and press-fitted into the small-diameter portion.
As a result, even when the V packing moves toward the second cylinder as the first piston slides when the piston main body advances, the C-shaped ring presses this, so that the first seal portion is securely sealed. Also, even if the V packing and the C-shaped ring move as the first piston slides, the ring retainer presses the C-shaped ring, so that the seal of the first seal portion is ensured and the fluid second seal portion Intrusion to the side can be prevented, and the situation where the air release path is blocked by the fluid is prevented. Therefore, it is possible to smoothly open the atmosphere when the fluid to the fluid supply pipe line again becomes non-flowing.

If necessary, the second seal portion includes a recess provided along the inner periphery of the inner surface of the second cylinder, and a V packing inserted into the recess. Sealing is ensured when the piston body is advanced.
Further, if necessary, a stopper is provided on the piston main body so as to stop the movement of the piston main body toward the second cylinder by stopping against the second step when the piston main body advances a predetermined stroke. Provided.
Excessive compression in the second cylinder chamber is prevented, and safety is achieved.

  According to the fluid pressure detection device of the present invention, the air release path for releasing the second cylinder chamber to the atmosphere when the piston body is retracted is provided. Therefore, when the fluid does not flow to the fluid supply pipe, the air in the second cylinder chamber Even if the gas expands or contracts, the air can enter and exit from the atmosphere open path, and the starting point of the pressure value does not change.Therefore, when the fluid flows, the piston body is not affected by temperature changes even in the advanced state. The pressure can be detected accurately.

  Hereinafter, based on an accompanying drawing, a fluid pressure detection device concerning an embodiment of the invention is explained in detail.

  1 to 6 show a fluid pressure detection device S according to the embodiment. This fluid pressure detection device S is provided in a fluid supply line (not shown) that supplies lubricating oil such as grease or oil to a desired location, and detects the pressure of the lubricating oil flowing through this fluid supply line. To do.

  The basic structure of the fluid pressure detection device S is a cylinder having a first cylinder 11 having one end connected to a fluid supply conduit through which lubricating oil flows and a second cylinder 12 communicating with the other end of the first cylinder 11. A piston main body 50 having a main body 10, a first piston 51 that is inserted into the first cylinder 11 so as to be movable back and forth, and a second piston 52 that is provided integrally with the first piston 51 and is inserted into the second cylinder 12. And comprising. And this fluid pressure detection apparatus S detects the pressure of the lubricating oil of a fluid supply line by detecting the air compression in the 2nd cylinder chamber 12a which changes with advance of the piston main body 50. FIG.

The first cylinder 11 has a hexagonal cross section. The first cylinder 11 has an inlet 13 formed at one end thereof, which communicates with the internal first cylinder chamber 11a and into which the lubricating oil of the fluid supply pipe flows, and is connected to the fluid supply pipe on the outer side of one end. A male screw 14 for connection is formed.
The first cylinder 11 has a small-diameter portion 15 formed on one end side thereof, on which the first piston 51 slides, and a first step portion 17 provided on the other end side of the small-diameter portion 15 with the axis line coaxial. And a large-diameter portion 16 formed so as to communicate with the small-diameter portion 15.

  The small diameter portion 15 includes a first seal portion 18 that seals the inner surface of the first cylinder 11 and the outer surface of the first piston 51. As shown in FIG. 3, the first seal portion 18 includes an inner wall of the first cylinder 11 and a first piston 51 in a packing storage portion 18 a in which the other end side of the first cylinder 11 of the small diameter portion 15 is hollowed out in a cylindrical shape. V-packing P1 that seals, C-shaped C-shaped ring 19 adjacent to the second cylinder 12 side of the V-packing P1, and the first cylinder 11 adjacent to the second cylinder 12 side of the C-shaped ring 19 And a ring presser 20 that is press-fitted into the frame.

The outer side of the V packing P1 of the first seal portion 18 is in sliding contact with the first piston 51, and is formed of a ring-shaped and V-shaped resin. The V-packing P <b> 1 of the first seal portion 18 is positioned such that the expansion side faces the one end side of the first cylinder 11.
The C-shaped ring 19 is formed of a resin such as plastic, and the outer diameter thereof is formed larger than the diameter of the packing storage portion 18 a, while the inner peripheral diameter is the inner peripheral surface of the first piston 51. Are formed in sliding contact with each other. Further, the C-shaped ring 19 is provided with an opening 21 formed by cutting out the C-shaped ring 19. Although the C-shaped ring 19 is hard to some extent, it can be bent to such an extent that the open ends 21a of the open portions 21 are brought into close contact with each other.
The ring retainer 20 is made of resin and has an outer peripheral diameter that is larger than the diameter of the packing storage portion 18 a, while an inner peripheral diameter thereof is in sliding contact with the outer peripheral surface of the first piston 51. Is formed.

  The large-diameter portion 16 is provided with a female screw portion 22 into which a first piston 51 and a second piston 52 of the piston body 50 are loosely inserted, and a male screw portion 23 provided in the second cylinder 12 described later is screwed. Yes.

  The second cylinder 12 has a circular cross section, and has a male screw portion 23 provided on one side of the second cylinder 12 with an axis coaxial with the axis of the first cylinder 11 and a female screw portion 22 of the first cylinder 11. And is connected to the first cylinder 11. The diameter of the second cylinder 12 is smaller than that of the large diameter portion 16 of the first cylinder 11 and communicates with the large diameter portion 16 via the second step portion 24. The second cylinder 12 seals the outer surface of the second piston 52 when the second piston 52 advances, and forms a gap 42 between the second piston 52 and the second piston 52 when the second piston 52 moves backward. A second seal portion 26 is provided.

  As shown in FIG. 4, the second seal portion 26 includes a concave portion 27 provided in an arc shape on the inner surface of the second cylinder 12 and a V packing P <b> 2 inserted into the concave portion 27. The V-packing P2 of the second seal portion 26 is formed in the same manner as the V-packing P1 of the first seal portion 18. The outer side of the V-packing P2 is slidably contacted with the outer side of the second piston 52, and the expansion side is the second. It is positioned toward the other side of the cylinder 12.

On the other side of the second cylinder 12, the compressed air in the second cylinder chamber 12a is detected via the tube end 30 and the tube 31 connected to the tube end 30, and the lubricating oil flowing through the fluid supply line is detected. A detection unit 35 for detecting pressure is provided.
The tube end 30 includes an air passage 32 provided inside and communicating with the second cylinder chamber 12 a, and an insertion portion 34 having a communication hole 33 communicating with the air passage 32 and inserted into the tube 31. Yes.
The tube end 30 is formed with a male screw 39 that is screwed into a female screw 38 formed on the inner surface of the other side of the second cylinder 12, and the male screw 39 is connected to the female screw of the second cylinder 12. It is screwed into 38 and connected to the second cylinder 12.
The insertion portion 34 is provided with a row of stepped portions that prevent the tube 31 from coming off in the axial direction of the outer peripheral surface thereof.
The tube 31 is made of a resin that is hard to some extent, and uses a tube that hardly deforms even when the air pressure rises inside.

The detection unit 35 includes a known pressure detection element (not shown) that is connected to the tube 31 and outputs an electrical signal corresponding to the air compression of the second cylinder 12, and a display unit that displays the lubricant pressure in a visible manner. 36 and a control unit (not shown) that receives the electrical signal and controls the display unit 36.
The display unit 36 is configured to include an LED array A composed of a plurality of LEDs 37 arranged in order of pressure values determined at predetermined intervals, and the LEDs 37 are turned on when energized to display the pressure values of the lubricating oil so as to be visible. .
The control unit receives the electrical signal output from the pressure sensing element, converts it into a pressure value signal corresponding to the pressure value determined at a predetermined interval, and selects the corresponding LED 37 of the LED array A based on this pressure value signal. It has a function to energize it.

The cylinder body 10 is provided with an atmosphere release path 40 that opens the second cylinder chamber 12a to the atmosphere when the piston body 50 is retracted.
The air release path 40 includes an open hole 43 provided in the large diameter portion 16 of the first cylinder 11, a large diameter portion 16 of the first cylinder 11, a clearance 41 provided in the second cylinder 12, and a second piston 52. And a gap 42 between the second seal portion 26 and the second seal portion 26.
The open hole 43 communicates from the inside of the large diameter portion 16 of the first cylinder 11 to the outside.
The clearance 41 is provided between the inner surface of the second cylinder 12 closer to the first cylinder 11 than the second seal portion 26 and the second piston 52.

The piston main body 50 is integrally formed with the axis of the first piston 51 and the axis of the second piston 52 being coaxial.
The first piston 51 is formed with a flange 53 that makes contact with the first step portion 17 when the piston body 50 is retracted.

A coil spring 54 that urges the piston main body 50 toward the first cylinder 11 is provided between the flange portion 53 and the second step portion 24.
The coil spring 54 is disposed with its axis coaxial with the axis of the piston body 50.
By this coil spring 54, the piston body 50 causes the retracted state in which the flange portion 53 of the first piston 51 stops against the first step portion 17, and the pressure of the lubricating oil is larger than the biasing force of the coil spring 54. Lubricating oil flows into the first cylinder chamber 11a, and the piston main body 50 is provided so as to be movable into two advanced states.

  Further, the first piston 51 of the piston main body 50 has a large-diameter portion 55 that faces the large-diameter portion 16 and expands the diameter thereof. The stepped portion of the enlarged diameter portion 55 and the second piston 52 stops against the second stepped portion 24 and stops moving the piston main body 50 toward the second cylinder 12 when the piston main body 50 advances a predetermined stroke. The stopper 55a is made possible.

  In the figure, reference numeral 60 denotes a rib having a hexagonal cross section for screwing the male screw portion 23 of the second cylinder 12 into the female screw portion 22 of the first cylinder 11 using a spanner or the like. An O-ring 62 that seals between the two cylinders 12 is an O-ring that seals between the first cylinder 11 and the fluid supply conduit.

When assembling the fluid pressure detection device S, for example, as shown in FIGS. 3 and 4, first, the first seal portion 18 and the second seal portion 26 are assembled.
In this assembly, the first seal portion 18 is inserted into the packing storage portion 18a of the small diameter portion 15 of the first cylinder 11, and the V packing P1 is inserted with the expansion side facing one end side of the first cylinder 11, and the C-shaped. The open end 21a of the open part 21 of the ring 19 is brought close to each other and inserted into the packing storage part 18a of the small diameter part 15 and the C-shaped ring 19 is brought into contact with the V packing P1 so that the ring retainer 20 is packed in the small diameter part 15 On the other hand, the second seal portion 26 is inserted into the recess portion 27 of the second cylinder 12 with the expanded portion being inserted toward the other side of the second cylinder 12 while being press-fitted into the storage portion 18a.
At this time, since the force acts in the separating direction of the open end 21a due to the rigidity of the C-shaped ring 19, the C-shaped ring 19 is stretched in the packing storage portion 18a. Therefore, the sealing performance is improved.

  Next, the first piston 51 of the piston main body 50 is inserted into the small diameter portion 15, the coil spring 54 is brought into contact with the flange portion 53 and stored in the large diameter portion 16, and the second cylinder 12 inserted through the O-ring is inserted. The male screw part 23 is screwed into the female screw part 22 of the large diameter part 16 to connect the first cylinder 11 and the second cylinder 12. Then, the tube end 30 is attached to the other side of the second cylinder 12, the tube 31 is attached to the tube end 30, and the detection unit 35 is attached to the tube 31 to assemble the fluid pressure detection device S.

When using the fluid pressure detecting device S, the first cylinder 11 is inserted through the O-ring in advance, and the first cylinder 11 is provided in a connection hole provided at a location where the fluid pressure in the fluid supply line is desired to be detected. The male screw 14 of the first cylinder 11 is screwed into the female screw.
In this state, lubricating oil is allowed to flow through the fluid supply line.
As shown in FIGS. 1A and 5, when there is a suspension period in which the lubricating oil does not flow in the fluid supply pipe, no pressure is generated in the lubricating oil in the fluid supply pipe, and therefore the piston body 50 is The flange portion 53 of the one piston 51 is in a retracted state in which it stops against the first step portion 17.

In this retracted state, when the second piston 52 is retracted, a gap 42 is formed between the outer surface of the second piston 52 and the inner surface of the second cylinder 12, and the second cylinder chamber 12a has an open hole 43, a clearance 41, and The atmosphere is opened to the atmosphere by the atmosphere opening path 40 formed by the gap 42. Therefore, even if there is a temperature change in the second cylinder chamber 12a and the air expands or contracts, the air enters and exits from the atmosphere release path 40, and the pressure change in the second cylinder chamber 12a does not occur.
Further, in this state, the open hole 43 and the gap 42 are communicated with each other via the clearance 41, so that the communication can be facilitated as compared with the case where the open hole 43 and the gap 42 are directly communicated.

  As shown in FIGS. 1B and 6, when the lubricating oil flows in the fluid supply line, pressure is generated in the lubricating oil in the fluid supply line, and this lubricating oil passes through the inflow port 13. The cylinder body 11a flows into the cylinder chamber 11a, the piston main body 50 enters the advanced state, the air in the second cylinder chamber 12a is compressed by the second piston 52, and the pressure detection element detects this compressed air and outputs an electrical signal. Based on the output electrical signal, the LEDs 37 of the LED array A of the display unit 36 are caused to emit light. In this state, the second seal portion 26 reliably seals the inner wall of the second cylinder 12 and the outer surface of the second piston 52. Therefore, air is sealed in the second cylinder chamber 12a, and air compression in the second cylinder chamber 12a is performed.

Further, at this time, since the second cylinder chamber 12a is opened to the atmosphere by the atmosphere release path 40 when the fluid does not flow to the fluid supply pipe line, there is no change in the starting point of the pressure value. Even in the advanced state, the pressure is accurately detected because it is not affected by the temperature change.
At this time, the fluid flowing into the first cylinder chamber 11a also flows between the inner peripheral surface of the small diameter portion 15 of the first cylinder 11 and the outer peripheral surface of the first piston 51, but the first seal portion. The inflow is restricted by 18. Therefore, it is possible to prevent the lubricating oil from entering the large-diameter portion 16, and the opening hole 43 is not blocked by the lubricating oil, so that the atmosphere can be smoothly released when it is not operating again.

In addition, when the piston main body 50 advances, even if the V packing P moves toward the second cylinder 12 as the first piston 51 slides, the C-shaped ring 19 continues to hold down this, so that the first seal portion 18 The seal is secure. Also, even if the V packing P and the C-shaped ring 19 move as the first piston 51 slides, the ring presser 20 presses the C-shaped ring 19 so that the seal of the first seal portion 18 is ensured. Lubricating oil can be prevented from entering the second seal portion 26 side, the atmosphere opening path 40 is not blocked by the lubricating oil, and the opening to the atmosphere is smooth when the fluid to the fluid supply line again becomes non-flowing. To be done.
At this time, even if the fluid supply line is abnormal and the pressure of the lubricating oil becomes excessively large, the stopper 55a of the enlarged diameter portion 55 of the piston main body 50 abuts on the second step portion 24 and the movement of the piston main body 50 is caused. Be stopped. Therefore, excessive compression in the second cylinder chamber 12a is prevented, and safety is achieved.

When the fluid supply pipe line is deactivated from the advanced state of the piston main body 50 and the lubricating oil does not flow into the fluid supply pipe line, the piston main body 50 is moved to the first cylinder 11 side by the coil spring 54, and The portion 53 stops against the first step portion 17 and the piston main body 50 is stopped, and is brought back again.
When the fluid does not flow through the fluid supply pipe, the piston main body 50 is forcibly moved to the first cylinder 11 side by the coil spring 54. Therefore, the inside of the second cylinder chamber 12a is quickly released to the atmosphere by the atmosphere release path 40, and the starting point state can be reliably ensured.
At this time, since the second cylinder chamber 12a is opened and closed using the second seal portion 26, the structure can be simplified and the atmosphere can be easily opened to the atmosphere.

  In the embodiment of the present invention, the open hole 43 is provided in the large-diameter portion 16, but the present invention is not limited to this, and may be communicated with the clearance 41 of the second cylinder 12. It is not limited to.

1 shows a fluid pressure detection device according to an embodiment of the present invention, where (a) shows a state when the piston body is retracted, and (b) shows a state when the piston body is advanced. It is a disassembled perspective view which shows the fluid pressure detection apparatus which concerns on embodiment of this invention. It is a figure which shows the principal part of the 1st cylinder of the fluid pressure detection apparatus which concerns on embodiment of this invention. It is a figure which shows the principal part of the 2nd cylinder of the fluid pressure detection apparatus which concerns on embodiment of this invention. It is a figure which shows the state at the time of reverse of the piston main body of the fluid pressure detection apparatus which concerns on embodiment of this invention. It is a figure which shows the state at the time of advance of the piston main body of the fluid pressure detection apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the conventional fluid pressure detection apparatus.

Explanation of symbols

S Fluid pressure detection device P1, P2 V packing A LED array 10 Cylinder body 11 First cylinder 11a First cylinder chamber 12 Second cylinder 12a Second cylinder chamber 13 Inlet port 14 Male screw 15 Small diameter portion 16 Large diameter portion 17 First Step portion 18 First seal portion 18a Packing storage portion 19 C-shaped ring 20 Ring retainer 21 Open portion 21a Open end 22 Female screw portion 23 Male screw portion 24 Second step portion 26 Second seal portion 27 Recess 30 Tube end 31 Tube 32 Ventilation path 33 Communication hole 34 Insertion part 35 Detection part 36 Display part 37 LED
40 Atmospheric release path 41 Clearance 42 Clearance 43 Opening hole 50 Piston body 51 First piston 52 Second piston 53 Gutter 54 Coil spring 55 Expanded diameter 60 Ribs 61, 62 O-ring

Claims (6)

A cylinder body having a first cylinder whose one end is connected to a fluid supply conduit through which fluid flows and a second cylinder communicating with the other end of the first cylinder, and is inserted into the first cylinder so as to be able to advance and retract. A first piston and a piston main body provided integrally with the first piston and having a second piston inserted through the second cylinder, and detecting air compression in the second cylinder chamber that changes as the piston main body advances. In the fluid pressure detecting device for detecting the pressure of the fluid in the fluid supply pipe line,
Set the air release path the second cylinder chamber is opened to the atmosphere during retraction of the piston body,
The first cylinder includes a first seal portion that seals an inner surface of the first cylinder and an outer surface of the first piston,
The second cylinder includes a second seal portion that seals an outer surface of the second piston when the second piston advances, and forms a gap with the second piston when the second piston moves backward,
An opening hole communicating with the gap between the second piston and the second seal portion is formed in the cylinder body, and the atmosphere opening path includes the gap and the opening hole. apparatus. A clearance is provided between the inner surface of the second cylinder closer to the first cylinder than the second seal portion and the second piston, the open hole is communicated with the clearance, and the air release path is defined as the gap, 2. The fluid pressure detecting device according to claim 1, wherein the fluid pressure detecting device includes a clearance and an open hole. The first cylinder is formed on one end side of the first cylinder with a small diameter portion on which the first piston slides and the first seal portion is provided, and on the other end side of the first cylinder via a first step portion. A large-diameter portion formed in communication with the small-diameter portion and into which the first piston and the second piston are loosely inserted.
The second cylinder is formed to have a smaller diameter than the large diameter portion of the first cylinder and communicate with the large diameter portion via a second step portion;
Forming a hook portion that stops at the first step portion when the first piston moves backward;
3. The fluid pressure detecting device according to claim 1, further comprising a coil spring that urges the piston body toward the first cylinder between the second step portion and the flange portion. The first seal portion includes a V packing provided on a small diameter portion of the first cylinder, a C-shaped ring provided on the second cylinder side of the V packing and fitted to the small diameter portion, and a first ring of the ring. 4. The fluid pressure detecting device according to claim 3, further comprising a ring presser provided on the two cylinder side and press-fitted into the small diameter portion. The said 2nd seal | sticker part was comprised including the recessed part provided along the inner periphery of the inner surface of the said 2nd cylinder, and the V packing inserted in this recessed part, It is comprised, 1 and 2, 3. The fluid pressure detection device according to 3 or 4. The piston body is provided with a stopper that stops the movement of the piston body toward the second cylinder by stopping against the second step when the piston body advances a predetermined stroke. The fluid pressure detection device according to claim 3, 4 or 5.

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