CN213699081U

CN213699081U - Differential pressure indicator

Info

Publication number: CN213699081U
Application number: CN202022201663.3U
Authority: CN
Inventors: 白琳; 刘志涛; 刘红梅; 付学豪
Original assignee: Sichuan Xinchuan Aviation Instrument Co ltd
Current assignee: Sichuan Xinchuan Aviation Instrument Co ltd
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2021-07-16
Anticipated expiration: 2030-09-30

Abstract

The utility model discloses a pressure differential indicator, including casing and slidable mounting piston in the casing, piston and casing are sealed and form high-pressure chamber and low-pressure chamber in seal position both sides, the piston is located the inherent first permanent magnet of one end in high-pressure chamber, slidable mounting has the signal cap isolated with high-pressure chamber on the casing, the signal cap has the second permanent magnet with the one end that the permanent magnet is relative, the piston is located the position of first permanent magnet and second permanent magnet actuation mutually when the pressure differential in high-pressure chamber and low-pressure chamber does not reach the default, the piston produces the displacement to the low pressure side and makes first permanent magnet and second permanent magnet repel each other in order to release the signal cap when the pressure differential in high-pressure chamber and low-pressure chamber reaches the default. The application provides a pressure differential indicator, when pressure differential is unusual, through popping out of signal cap in order to carry out mechanical warning, mechanical structure is reliable and stable, has avoided the warning ageing that the signal indication lamp damage arouses, has improved pressure differential indicator's reliability.

Description

Differential pressure indicator

Technical Field

The utility model relates to a pressure differential signaling ware technical field, more specifically say, relate to a pressure differential indicator.

Background

After the fuel filter is used for a period of time, the filtered impurities are gradually accumulated and attached to the surface of the filter element, so that the resistance of the filter element is increased, if the filter element cannot be replaced or cleaned in time, the power of an engine is reduced, and the engine cannot be normally used seriously. However, the period of replacing or cleaning the fuel filter mainly depends on subjective judgment of a user, and the filter element is replaced or cleaned regularly according to experience, so that the blockage condition of the fuel filter element cannot be accurately judged, and two conditions can be caused: firstly, the filter element is replaced in advance without reaching the service life, thereby causing unnecessary waste; secondly, the filter element reaches the service life and is not replaced in time, so that the normal work of the engine is influenced. Therefore, the blockage condition of the filter element of the filter is judged by using a mechanical differential pressure sensor at present according to the differential pressure of the oil inlet end and the oil outlet end of the filter.

The common differential pressure sensor usually adopts a mechanical piston type structure to sense pressure, and when the differential pressure is lower than an indicated value, a differential pressure annunciator is not started; when the pressure difference reaches or is higher than the indicated value, the pressure difference annunciator is started, the micro switch is switched on, and the signal indicator lamp is switched on to warn that the pressure difference is too high. However, the signal indicator light may be damaged, which results in low reliability of the differential pressure annunciator, and if the technician fails to notice the warning signal in time, it is easy to cause the related equipment in the high-pressure chamber to be damaged under high pressure.

In summary, how to effectively solve the problems of low warning reliability of the differential pressure indicator through the indicator light and the like is a problem to be solved by those skilled in the art.

SUMMERY OF THE UTILITY MODEL

In view of this, the present invention provides a pressure difference indicator, the structural design of which can effectively solve the problem of low reliability of the pressure difference indicator when the pressure difference indicator is warned by an indicating lamp.

In order to achieve the above object, the utility model provides a following technical scheme:

the utility model provides a pressure difference indicator, includes casing and slidable mounting in piston in the casing, the piston with the casing is sealed and forms high-pressure chamber and low pressure chamber in sealed position both sides, the piston is located the inherent first permanent magnet of one end in high-pressure chamber, slidable mounting has on the casing with the isolated signal cap in high-pressure chamber, the signal cap with the one end that the permanent magnet is relative has the second permanent magnet, the high-pressure chamber with when the pressure differential in low pressure chamber does not reach the default the piston is located the position of first permanent magnet and second permanent magnet looks actuation, the high-pressure chamber with when the pressure differential in low pressure chamber reaches the default the piston produces to the displacement of low pressure side and makes first permanent magnet and second permanent magnet repel each other in order will the signal cap is released.

Preferably, in the above differential pressure indicator, the first permanent magnet is a permanent magnet ring, and the second permanent magnet is a magnetic steel sleeved in the permanent magnet ring.

Preferably, in the above differential pressure indicator, the permanent magnet ring and the magnetic steel have the same magnetic pole direction.

Preferably, in the above differential pressure indicator, the housing is fixedly connected to a rear cover, and an elastic member for pushing the piston to move to a high pressure side is disposed between the rear cover and the piston.

Preferably, in the above differential pressure indicator, the housing includes an upper housing and a lower housing that are fixedly connected, the piston is installed in the lower housing, a top end of the lower housing protrudes upward and forms a groove therein, a bottom end of the signal cap is sleeved outside the protrusion, and a top end of the piston is located in the groove.

Preferably, in the above differential pressure indicator, the upper case and the lower case are coupled by a pin.

Preferably, in the above differential pressure indicator, a locking component for locking the signal cap in the retracted position when the temperature is lower than the first preset temperature and unlocking when the temperature reaches the second preset temperature is further disposed in the housing.

Preferably, in the above differential pressure indicator, the locking member is a temperature sensing clamp, and an end of the temperature sensing clamp is internally buckled to clamp the signal cap when the temperature is lower than the first preset temperature, and is deformed to release the signal cap when the temperature reaches the second preset temperature.

Preferably, in the above differential pressure indicator, a transmission member and a microswitch are further arranged in the housing, the transmission member is fixedly connected to the signal cap, and when the signal cap is pushed out, the transmission member acts on a contact of the microswitch to turn on the microswitch to output an on signal.

Preferably, in the above differential pressure indicator, the transmission member is a lever plate, one end of the lever plate is fixedly connected to the signal cap, and the other end of the lever plate is used for pressing a contact of the microswitch.

The utility model provides a pressure differential indicator includes casing, piston and signal cap. The piston is slidably mounted in the shell, the piston and the shell are sealed, a high-pressure cavity and a low-pressure cavity are formed in two sides of the sealed position, the piston is fixedly provided with a first permanent magnet at one end of the high-pressure cavity, a signal cap isolated from the high-pressure cavity is slidably mounted on the shell, a second permanent magnet is arranged at one end, opposite to the permanent magnet, of the signal cap, the piston is located at the position where the first permanent magnet and the second permanent magnet are attracted when the pressure difference between the high-pressure cavity and the low-pressure cavity does not reach a preset value, and when the pressure difference between the high-pressure cavity and the low-pressure cavity reaches the preset value, the piston generates displacement towards the low-pressure side and enables the first.

Use the utility model provides a pressure differential indicator, signal cap pass through the cooperation of the first permanent magnet on second permanent magnet and the piston. When the pressure difference between the high-pressure cavity and the low-pressure cavity does not reach a preset value, the piston is located at the attraction position of the first permanent magnet and the second permanent magnet, so that the signal cap can be attracted to the retraction position magnetically. When the pressure difference between the high-pressure cavity and the low-pressure cavity reaches a preset value, the piston displaces towards the low-pressure side, so that the acting force of the first permanent magnet and the acting force of the second permanent magnet overturn to become repulsive force in the opposite direction, and the signal cap is pushed out under the action of the repulsive force to achieve the purpose of mechanical alarm indication. To sum up, the application provides a pressure differential indicator, when pressure differential is unusual, through popping out of signal cap in order to carry out mechanical warning, mechanical structure is reliable and stable, has avoided the warning ageing that the signal indicator damage arouses, has improved pressure differential indicator's reliability.

In a preferred embodiment, the shell is also provided with a transmission piece and a microswitch, the transmission piece is fixedly connected with the signal cap, and when the signal cap is pushed out, the transmission piece acts on a contact of the microswitch to switch on the microswitch so as to output an on signal. Therefore, when the pressure difference is abnormal, the mechanical warning is carried out through the ejection of the signal cap, and meanwhile the micro switch outputs an on signal to finish the output of the alarm signal of the electric indicating part. The pressure difference indicator has mechanical and electrical output, realizes simultaneous indication and alarm of dual signals, has a redundant signal output design, reduces the probability of product function failure, and can meet different requirements in multiple aspects.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic structural view of a differential pressure indicator according to an embodiment of the present invention.

The drawings are numbered as follows:

1. an upper shell; 2. a signal cap; 3. a temperature sensing clamp; 4. a lower case; 5. a piston; 6. an elastic member; 7. a rear cover; 8. a lever plate; 9. a microswitch; 10. a socket; 11-12, sealing rings; 13. a screw; A. a high pressure chamber; B. a low pressure chamber.

Detailed Description

The embodiment of the utility model discloses pressure difference indicator to improve the reliability of warning.

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a differential pressure indicator according to an embodiment of the present invention.

In one embodiment, the present invention provides a differential pressure indicator comprising a housing, a piston 5, and a signal cap 2.

Wherein, piston 5 slidable mounting is in the casing, and piston 5 and casing sealed and form high pressure chamber A and low pressure chamber B in sealed position both sides. That is, the piston 5 is used to form a high pressure chamber a and a low pressure chamber B inside the product, and specifically, the housing may be perforated to communicate the high pressure chamber a with the high pressure of the environment and the low pressure chamber B with the low pressure of the environment. The manner in which the piston 5 seals against the inner wall of the housing is not limited herein.

The piston 5 is slidably mounted in the housing so that it can move along the housing under the pressure differential between the high pressure chamber a and the low pressure chamber B. That is, when the pressure difference between the high pressure chamber a and the low pressure chamber B does not reach the preset value, the piston 5 is located at the first position, for example, the corresponding top end position in fig. 1, and when the pressure difference between the high pressure chamber a and the low pressure chamber B reaches the preset value, for example, the pressure difference indicator is used in cooperation with the oil filter of the hydraulic system, and is used for indicating the blockage of the filter element, when the pressure difference between the oil filter high pressure chamber a and the low pressure chamber B reaches the preset value, the piston 5 moves from the high pressure side to the low pressure side, and moves downward for a certain distance as shown in fig. 1.

The shell is provided with a signal cap 2 isolated from the high-pressure cavity A in a sliding mode, the signal cap 2 is isolated from the high-pressure cavity A, the signal cap and the high-pressure cavity A can be isolated from each other through the shell, and the signal cap and the high-pressure cavity A can be isolated from each other through a sealing component. The signal cap 2 is slidably mounted on the housing, meaning that it can move linearly relative to the housing and cannot be removed from the housing.

The piston 5 is located the inherent first permanent magnet of one end in high pressure chamber A, and the signal cap 2 has the second permanent magnet with the opposite one end of permanent magnet, and the first permanent magnet cooperates with the second permanent magnet to realize the retraction or the pop-up of signal cap 2. Specifically, when the differential pressure between the high pressure chamber a and the low pressure chamber B does not reach the preset value, the piston 5 is located at a position where the first permanent magnet and the second permanent magnet are attracted, and when the differential pressure between the high pressure chamber a and the low pressure chamber B reaches the preset value, the piston 5 generates displacement to the low pressure side and enables the first permanent magnet and the second permanent magnet to repel each other so as to push out the signal cap 2. It should be noted that the high pressure side and the low pressure side referred to herein and hereinafter refer to the directions of high pressure and low pressure that correspond to the high pressure chamber and the low pressure chamber. Specifically, the magnetic pole direction and the relative position relationship of the first permanent magnet and the second permanent magnet may be set so as to satisfy the above interaction. It should be noted that, when the pressure difference between the high pressure chamber a and the low pressure chamber B does not reach the preset value, the piston 5 is located at the attraction position of the first permanent magnet and the second permanent magnet, and the signal cap 2 can be reset by pressing the signal cap with an external force and the first permanent magnet and the second permanent magnet are attracted, so the signal cap 2 is in the retraction state under the action of the magnetic attraction.

A sealing ring can be arranged outside the shell to realize the sealing installation of the differential pressure indicator.

Use the utility model provides a pressure differential indicator, signal cap 2 pass through the cooperation of the first permanent magnet on second permanent magnet and the piston 5. When the pressure difference between the high pressure cavity A and the low pressure cavity B does not reach a preset value, the piston 5 is positioned at the attraction position of the first permanent magnet and the second permanent magnet, so that the signal cap 2 can be magnetically attracted to the retraction position. When the pressure difference between the high-pressure cavity A and the low-pressure cavity B reaches a preset value, the piston 5 generates displacement towards the low-pressure side, so that the acting force of the first permanent magnet and the second permanent magnet is overturned to become repulsive force in the opposite direction, and the signal cap 2 is pushed out under the action of the repulsive force to achieve the purpose of mechanical alarm indication. In conclusion, the pressure difference indicator provided by the application is when pressing the difference, through popping up of signal cap 2 in order to carry out mechanical warning, mechanical structure is reliable and stable, has avoided the warning ageing that the signal indication lamp damage arouses, has improved pressure difference indicator's reliability.

Specifically, the first permanent magnet is a permanent magnet ring, and the second permanent magnet is magnetic steel sleeved in the permanent magnet ring. By sleeving the permanent magnet ring in the magnetic steel, when the magnetic steel moves up and down along the axis of the permanent magnet ring, the interaction between the magnetic steel and the permanent magnet ring is switched between repulsion and attraction along with different positions. Further, the magnetic pole directions of the permanent magnet ring and the magnetic steel are the same. If one end of the high-voltage side is an N pole, the other side is an S pole, the position of the permanent magnet ring is staggered with the position of the magnetic steel, so that the opposite parts of the magnetic poles of the permanent magnet ring and the magnetic steel are opposite, and suction can be formed between the permanent magnet ring and the magnetic steel; along with the synchronous movement of the magnetic steel and the piston 5, the permanent magnetic ring and the magnetic steel are opposite in position, so that the same magnetic poles of the permanent magnetic ring and the magnetic steel are opposite, and repulsion is formed between the permanent magnetic ring and the magnetic steel to push the signal cap 2 out. The first permanent magnet is not limited to a permanent magnet ring, and a combination of one or more permanent magnets may be used. The second permanent magnet is not limited to magnetic steel, and can be provided as a combination of one or more permanent magnets according to requirements.

In the above embodiment, the housing is fixedly connected with the rear cover 7, and the elastic member 6 for pushing the piston 5 to move to the high pressure side is arranged between the rear cover 7 and the piston 5. The elastic member 6 may be a spring, such as a compression spring having two ends respectively abutting against the rear cover 7 and the piston 5, or other parts capable of providing a damping force. By the arrangement of the elastic member 6, the elastic member 6 is deformed by being acted on when the piston 5 moves, and thus, the elastic force of the elastic member 6 needs to be overcome. When the pressure difference between the high pressure chamber A and the low pressure chamber B is larger than the acting force of the elastic member 6, the piston 5 is pushed to move. Therefore, the pre-tightening force of the elastic piece 6 is used for setting a preset value for controlling the pushing piston 5 to move corresponding to the pressure difference, namely the pre-tightening force of the elastic piece 6 is used for setting the adjustment of the warning pressure value. The pretightening force of the elastic piece can be controlled through the structure of the elastic piece. Because the pretightening force of the elastic piece 6 is generally far greater than the acting force of the first permanent magnet and the second permanent magnet, the influence of the acting force of the first permanent magnet and the second permanent magnet on the preset value of the pressure difference can be ignored. Of course, the influence of the acting force of the first permanent magnet and the second permanent magnet can be introduced into the control of the preset value in a debugging mode and the like. The elastic member 6 may not be provided according to the setting of a specific pressure difference preset value.

In order to facilitate the installation of each part, the casing includes fixed connection's epitheca 1 and inferior valve 4, and piston 5 installs in inferior valve 4, and the top of inferior valve 4 is upwards protruding and inside formation recess, and outside the arch was located to the bottom pot head of signal cap 2, the top of piston 5 was located the recess. That is, signal cap 2 can slide along bellied outer wall, and piston 5 can slide along bellied inner wall, realizes completely cutting off through protruding between signal cap 2 and the high-pressure chamber A, and the magnetic force of first permanent magnet and second permanent magnet acts on and sees through bellied wall with interact. The shell adopts the structure, so that the assembly of each part is convenient, and the piston 5 and the signal cap 2 can be well matched. Specifically, the upper shell 1 and the lower shell 4 are connected through the pins, so that the connection is reliable and the structure is simple. The upper case 1 and the lower case 4 may be connected by other conventional fixing means such as bolts, if necessary. In the case of a rear cover 7, the rear cover 7 is fixedly connected to the lower shell 4, in particular in a crimping manner.

In the above embodiments, a locking means for locking the signal cap 2 in the retracted position when the temperature is lower than the first preset temperature and unlocking when the temperature reaches the second preset temperature is further provided in the housing. That is, by setting the locking component, when the temperature is lower than the first preset temperature, the signal cap 2 is locked, i.e. no warning is given. And only when the temperature reaches the second preset temperature, the locking component releases the signal cap 2, so that the signal cap 2 can pop up a warning when the pressure difference reaches the preset value according to the pressure difference between the high-pressure cavity A and the low-pressure cavity B. The specific first preset temperature is less than or equal to the second preset temperature, and the specific value is set according to the use environment of the differential pressure indicator, which is not limited herein. In summary, the temperature locking function of the signal cap 2 is realized through the arrangement of the locking component.

Specifically, locking part is temperature sensing clamp 3, and the tip of temperature sensing clamp 3 is interior the knot when the temperature is less than first preset temperature in order to cramp signal cap 2, warp in order to release signal cap 2 when the temperature reaches the second preset temperature. The temperature sensing clamp 3 may be made of alloy that deforms with temperature, and the material may be conventional material with the above properties in the prior art according to the preset temperature. When the temperature is lower than the first preset temperature, the end part inner buckle hoops the signal cap 2, and the locking of the signal cap 2 is realized. And when the temperature reaches a second preset temperature, the end of the temperature sensing clamp 3 is deformed, such as from an inner buckle to a straight shape, thereby releasing the signal cap 2.

On the basis of the above embodiments, the shell is also provided with a transmission member and a microswitch 9, the transmission member is fixedly connected with the signal cap 2, and when the signal cap 2 is pushed out, the transmission member acts on a contact of the microswitch 9 to switch on the microswitch 9 and output an on signal. The transmission part is a switching mechanism between oil hydraulic pressure and the microswitch 9, the pushing-out and retracting displacement of the signal cap 2 is transmitted to the microswitch 9 through the arrangement of the transmission part, the transmission part acts on a contact of the microswitch 9 when the signal cap 2 is pushed out to switch on the microswitch 9 and output an on signal, and correspondingly, the transmission part releases the contact of the microswitch 9 after the signal cap 2 retracts to disconnect the microswitch 9 and does not output the on signal any more. Through realizing the output of the switching electric signal for the microswitch 9, when the pressure difference is abnormal, not only the mechanical warning is carried out through the popping-up of the signal cap 2, but also the microswitch 9 outputs an on signal to finish the output of the alarm signal of the electric indicating part. The pressure difference indicator has mechanical and electrical output, realizes simultaneous indication and alarm of dual signals, has a redundant signal output design, reduces the probability of product function failure, and can meet different requirements in multiple aspects. For the structure and the working principle of the microswitch 9, reference is made to the prior art, and the details are not repeated herein.

In addition, when the pressure difference indicator is used for oil filtration of a hydraulic system, convenience in ground service inspection of oil circuit pollution conditions can be guaranteed through mechanical indication, so that the requirement on transition or inspection time before flight is met, and the rapid movement of an airplane is guaranteed; and the real-time data acquisition requirement of the airborne health management system can be met through the output of the electric signals.

Specifically, the transmission piece is a lever piece 8, one end of the lever piece 8 is fixedly connected with the signal cap 2, and the other end of the lever piece is used for pressing a contact of the microswitch 9. Namely, the middle part of the lever sheet 8 is rotationally connected with the shell or the shell of the microswitch 9, and one end of the lever sheet 8 is fixedly connected with the signal cap 2. When the signal cap 2 is pushed out, the other end of the lever sheet 8 presses the contact of the microswitch 9 to be connected; when the signal cap 2 retracts, the other end of the lever piece 8 is lifted to turn off the microswitch 9. The lever sheet 8 has simple transmission structure and reliable transmission. The transmission piece can also adopt other conventional transmission parts such as a connecting rod assembly and the like according to requirements.

The differential pressure indicator applied to the oil filter of the hydraulic system is specifically described as an example.

The differential pressure indicator is matched with the oil filter of the hydraulic system for use and is used for indicating the pollution of the oil filter. When the pressure difference between the oil filter high-pressure cavity A and the oil filter low-pressure cavity B reaches a preset value and the temperature reaches the alarm temperature range, a mechanical indication that the signal cap 2 pops up is given, and meanwhile, a switching electric signal indication is output.

Specifically, the differential pressure annunciator adopts a mechanical piston 5 type structure as shown in fig. 1, and when the temperature and oil hydraulic pressure difference is a normal value, the signal cap 2 is kept in a reset state under the action of the piston 5; when the temperature is higher than the given temperature by 18 ℃, the locking component is opened, and the oil hydraulic pressure difference reaches a preset value (0.5 +/-0.05) MPa, the oil hydraulic pressure pushes the piston 5 to move, so that the piston and the signal cap 2 move away for a certain distance, at the moment, the action between the permanent magnetic ring on the signal cap 2 and the magnetic steel on the piston 5 is overturned, and the repulsion in the opposite direction is changed, so that the signal cap 2 is popped up, and the purpose of mechanical alarm indication is achieved; at the same time, the action of the mechanical indication end signal cap 2 drives the lever piece 8 connected with the end of the signal cap 2 to do lever motion, so that the other end of the lever piece 8 touches the contact of the electric microswitch 9. Through the popping and resetting of the signal cap 2, the on-off function of the microswitch 9 is realized in a linkage way, and the on-off alarm signal output of the electric indication part is completed. In addition, the product has the temperature locking function, and when the temperature is lower than 0 ℃, the temperature sensing assembly is locked, and the signal cap 2 assembly is locked after being reset.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The utility model provides a pressure difference indicator, its characterized in that, including casing and slidable mounting in piston in the casing, the piston with the casing is sealed and forms high-pressure chamber and low pressure chamber in sealing position both sides, the piston is located the inherent first permanent magnet of one end in high-pressure chamber, slidable mounting has on the casing with the isolated signal cap in high-pressure chamber, the signal cap with the one end that the permanent magnet is relative has the second permanent magnet, the high-pressure chamber with when the pressure differential in low pressure chamber does not reach the default the piston is located the position of first permanent magnet and second permanent magnet looks actuation, the high-pressure chamber with when the pressure differential in low pressure chamber reaches the default the piston produces to the displacement of low pressure side and makes first permanent magnet and second permanent magnet repel each other in order will the signal cap is released.

2. The differential pressure indicator of claim 1, wherein the first permanent magnet is a permanent magnet ring and the second permanent magnet is magnetic steel disposed within the permanent magnet ring.

3. A differential pressure indicator as claimed in claim 2 wherein the permanent magnet ring and the magnetic steel have the same magnetic polarity.

4. The differential pressure indicator of claim 1, wherein a rear cover is fixedly connected to the housing, and an elastic member for pushing the piston to move to a high pressure side is disposed between the rear cover and the piston.

5. The differential pressure indicator of claim 1, wherein the housing comprises an upper shell and a lower shell fixedly connected to each other, the piston is mounted in the lower shell, a top end of the lower shell protrudes upward and forms a groove therein, a bottom end of the signal cap is sleeved outside the protrusion, and a top end of the piston is located in the groove.

6. The differential pressure indicator of claim 5, wherein the upper shell and the lower shell are joined by a dowel.

7. A differential pressure indicator as claimed in any one of claims 1 to 6, wherein a locking means is provided within the housing for locking the signalling cap in the retracted position when the temperature is below a first predetermined temperature and for unlocking when the temperature reaches a second predetermined temperature.

8. The differential pressure indicator of claim 7, wherein the locking member is a temperature sensitive clip, an end of the temperature sensitive clip being configured to snap-fit to clamp the signaling cap when the temperature is below the first predetermined temperature and to deform to release the signaling cap when the temperature reaches the second predetermined temperature.

9. The differential pressure indicator according to any one of claims 1-6, wherein a transmission member and a micro switch are further disposed in the housing, the transmission member is fixedly connected to the signal cap, and when the signal cap is pushed out, the transmission member acts on a contact of the micro switch to turn on the micro switch to output an on signal.

10. The differential pressure indicator of claim 9, wherein the transmission member is a lever plate, one end of the lever plate is fixedly connected to the signal cap, and the other end of the lever plate is used for pressing a contact of the micro switch.