JPH025256B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overpressure protection device for fluid pressure equipment,
In particular, it relates to a device suitable for protecting precision water pressure gauges from excessive pressure (hereinafter referred to as "overpressure").

In order to protect fluid pressure devices such as water pressure gauges and hydraulic or pneumatically actuated control elements from overpressure, elastic protection means such as coil springs or deformation of diaphragms have conventionally been used. For example, a discharge valve closed by a coil spring is attached to the sealed liquid container of a water pressure gauge, and when the overpressure exceeds the elastic closing force of this coil spring, the discharge valve is opened and the sealed liquid is discharged. Protect the water pressure sensing element from overpressure. Alternatively, a part of the filled liquid container is closed with an elastic diaphragm shaped to recess outward from the container, and in case of overpressure exceeding the elastic closing force inherent to the diaphragm, the diaphragm is moved outward from the container. It is bent back to release the increase in fluid pressure of the filled fluid.

However, conventional elastic protection means for fluid pressure equipment incorporate coil springs and the like as elastic elements, resulting in complicated structures and increased manufacturing costs.
There were drawbacks such as the troublesome setting of the operating point.

The present invention seeks to overcome the above-mentioned drawbacks of the prior art. To achieve this objective, the present invention uses a flexible gas container containing gas and utilizes compression of the flexible gas container by overpressure for overpressure protection. In one embodiment of the present invention, a rigid housing in which a hollow portion is formed to serve as a variable pressure chamber in contact with a pressure receiving surface of a fluid pressure device is attached to a pressure receiving portion of a fluid pressure device, and a small gap is formed from the pressure receiving surface of the housing. The protective diaphragm is then fixed to the housing to define a chamber between the housing pressure receiving surface and the protective diaphragm.
A pore through the housing wall connects the chamber to the variable pressure chamber. A flexible gas container containing gas at a protective lower limit pressure is arranged in the variable pressure chamber, and expansion of the container is limited by an expansion limiting wall of the rigid housing. The space from the small chamber through the pores to the variable pressure chamber is filled with the sealed liquid.

Normally, the external pressure acting on the protective diaphragm is transmitted to the sealed liquid via the protective diaphragm, and the pressure of the sealed liquid is applied to the pressure receiving surface of the fluid pressure device to perform the required function. At this time,
Although the pressure of the sealed liquid in the variable pressure chamber is lower than the gas pressure in the gas container, the volume of the gas container is kept constant by the expansion limiting wall. If the pressure applied from the outside via the protective diaphragm exceeds the protective lower limit pressure even by a small amount, the overpressure is transmitted to the filling liquid of the variable pressure chamber, compressing the gas container and reducing its volume. Therefore, the volume of the variable pressure chamber outside the gas container increases, the liquid sealed in the small chamber enters the variable pressure chamber, and the protective diaphragm is brought into close contact with the pressure receiving surface of the housing due to the external pressure. Therefore, any overpressure after the close contact is prevented by the rigid housing wall and not transmitted to the variable pressure chamber, and the pressure receiving surfaces and internal elements of the fluid pressure device are protected from the overpressure.

When the external pressure acting on the protection diaphragm drops below the protection lower limit pressure, the above-mentioned constant operation is automatically restored.

Hereinafter, the present invention will be described in detail with reference to an overpressure protection device for a hydraulic pressure detector shown in the accompanying drawings, but the application of the present invention is not limited to hydraulic pressure detectors. FIG. 1 shows a longitudinal sectional view of an embodiment of the invention. The hydraulic pressure detector 1 in the illustrated example has a pressure detection unit 10 fixed in a sealed liquid L in a container 11,
The pressure receiving diaphragm 12 is stretched in contact with the liquid surface of the sealed liquid L, and its periphery is fixed to the container 11. The input voltage and electrical output of the pressure sensing unit 10 are connected via leads 13 to a power supply and amplifier circuit 14. In principle, the pressure receiving diaphragm 12 transmits the fluid pressure applied to its pressure receiving surface 12A to the sealed liquid L without loss, and the pressure detection unit 10 detects the pressure of the sealed liquid L. The pressure detection unit 10 itself is well known, and is composed of, for example, an element utilizing a piezoresistive effect. The hydraulic pressure detector 1 is also known.

The overpressure protection device 2 includes a pressure receiving surface 1 of the hydraulic pressure detector 10.
It has a housing 21 defining a variable pressure chamber 20 in contact with 2A. The variable pressure chamber 20 includes a housing 21
is a hollow internal space in which a gas container 25, which will be described below, is placed. The housing 21 consists of an upper lid part 211 and a bowl-shaped part 213, both of which are integrated by welding at their outer edges 212. The upper lid 211 has a cylindrical hanging portion 211B, from which the flexible gas container 25 is suspended and fixed. A small chamber 23 is defined between the pressure receiving surface 211A and the protective diaphragm 22 by extending the protective diaphragm 22 from the upper lid pressure receiving surface 211A of the housing 21 through a small gap d and welding its peripheral edge to the upper lid 211. . This small chamber 23 is communicated with the upper space 20A of the variable pressure chamber 20 through a pore 24 provided in the upper lid 211.

A flexible gas container 25 containing gas A at a protection lower limit pressure p _c (see FIG. 2) at which the protection operation is to be started is arranged within the variable pressure chamber 20 . The gas container 25 in the illustrated embodiment includes a bowl-shaped portion 26 and a diaphragm 27 as a flexible wall that closes the opening of the bowl-shaped portion 26. The diaphragm 27 and the bowl-shaped portion 26 are collectively fixed at the outer periphery to the outer periphery of the hanging portion 211B of the housing upper lid 211 by welding to form a flexible gas container 25. The upper space 20A of the variable pressure chamber 20 between the inner surface of the top wall of the housing 21 and the diaphragm 27 communicates with the lower space 20B of the variable pressure chamber 20 through a through hole 211C provided in the housing upper lid hanging portion 211B. The manufacturing order is to attach the flexible metal tube 28 to the bowl-shaped part 26, and then attach the gas container 2.
While maintaining the inside of the housing at atmospheric pressure, the bowl-shaped portion 26 and the diaphragm 27 are collectively removed from the housing upper lid 211.
Then, pressurized gas A such as compressed air at a predetermined pressure is fed into the gas container 25 through the pipe 28, and one end of the pipe 28 is sealed to seal the sealed part 2.
9 to seal the gas container 25. At this time, the center portion of the diaphragm 27 contacts the expansion limiting wall 30 provided at the center of the lower end of the housing upper lid 211 with a sufficiently large contact area, and even if the outside pressure of the container 25 is lower than the pressure of the pressurized gas A, the diaphragm 27 27 is prevented from deflecting in the direction of expansion of the container 25. Therefore, below the pressure of the pressurized gas A in the gas container 25, the variable pressure chamber 20
The pressure inside can be varied without changing the volume of the variable pressure chamber 20.

In order to prevent the external pressure of the hydraulic pressure detector 1 from being applied directly to the pressure receiving surface 12A without going through the overpressure protection device 2, the contact surface between the hydraulic pressure detector 1 and the overpressure protection device 2 is provided with a Insert the packing 31 and then attach the overpressure protection device 2 to the hydraulic pressure detector 1 with the screw 32.
and seal the joint between the two.

The solid line in FIG. 2 indicates the flexible gas container 2 having the above configuration.
5 shows the relationship between the volume V of No. 5 and the pressure p in the variable pressure chamber 20. The pressurized air A in the gas container 25 is at the protection lower limit pressure.
Since the diaphragm 27 of the gas container 25 is in contact with the expansion limiting wall 30 as described above, when the pressure inside the variable pressure chamber 20 is below the protection lower limit p _c , the gas container ₂₅ The volume V of 25 is a constant value
V is kept at ₀ . When the pressure inside the fluctuating pressure chamber 20 increases beyond the protection lower limit pressure p _c , the volume V of the gas container 25 becomes equal to the pressure inside the fluctuating pressure chamber 20 due to the deflection of the diaphragm 27 . It is reduced in size as shown by the dotted line 27A in FIG. Assuming that the pressurized gas A is an ideal gas, this compression follows the Boyle-Charles law.

The operation of the overpressure protection device of the present invention having the above structure will be explained. When the external pressure P applied to the protective diaphragm 22 is lower than the protection lower limit pressure p _c , that pressure is transmitted to the sealed liquid L in the variable pressure chamber 20 via the protective diaphragm 22 , and is further transferred to the pressure receiving pressure of the liquid pressure detector 1 . It is added to surface 12A. Therefore, the hydraulic pressure detector 1
performs normal hydraulic pressure detection as long as the external pressure applied to the protection diaphragm 22 is below the protection lower limit pressure p _c .

When the external pressure P applied to the protective diaphragm 22 exceeds the protection lower limit pressure p _c , the volume V of the gas container 25 is compressed and reduced as shown in FIG. This is because the pressure within the variable pressure chamber 20 exceeds the protection lower limit pressure p _c . When the amount of change ΔV in the volume V becomes equal to the volume of the small chamber 23, all of the sealed liquid L in the small chamber 23 moves to the variable pressure chamber 20. Therefore, the protective diaphragm 22 is connected to the pressure receiving surface 211A of the housing upper lid 211.
In close contact. For this reason, even if the protective diaphragm 2
Even if the external pressure P applied to 2 further increases, that external pressure is only applied to the rigid wall of the housing 21, and the pressure of the sealed liquid L in the variable pressure chamber 20 increases by a pressure increment corresponding to the volume change ΔV. It is maintained at the sum of Δp and the protection lower limit p _c (p _c +Δp). Therefore, the volume of the gas container 25 is also indicated by the chain line in FIG.
−ΔV). Further, the pressure applied to the pressure receiving surface 12A of the hydraulic pressure detector 1 is transmitted through the protective diaphragm 22.
No matter how high the external pressure P applied to the housing upper cover 211 increases beyond the above (p _c +Δp),
As long as the pressure is not destroyed, the pressure is kept constant at (p _c +Δp), and the pressure detection unit 10 is protected from overpressure.

If the pressure change Δp is designed to be sufficiently smaller than the protection lower limit pressure p _c , a pressure that substantially exceeds the protection lower limit pressure p _c will be applied to the pressure detection unit 10 of the hydraulic pressure detector 1. will disappear.

When the overpressure disappears and the external pressure P applied to the protective diaphragm 22 becomes lower than the protective lower limit pressure p _c , as is clear from FIG. 2, the volume V of the gas container 25 expands and the sealed liquid L returns to the small chamber 23. Enter small room 2
3 and the pressure inside the variable pressure chamber 20 become equal to the external pressure P, and the hydraulic pressure detector 1 resumes normal pressure detection.
That is, the overpressure protection device 2 according to the present invention is of an automatic return type.

EXAMPLE An overpressure protection device 2 having the structure shown in FIG. 1 was prototyped for a water pressure detector 1 having a measurement range of 0-1.0 kg/cm ² . The housing 21 is made of stainless steel with an outer diameter of 32 mm and an inner diameter of 27 mm.
mm, cylindrical shape with a height of 9 mm, and a diameter of 0.3 mm on the top wall.
Eight pores were drilled. The gas container and each diaphragm were all made of stainless steel. Silicone oil was introduced as a filling liquid by a vacuum filling method through the oil filling hole 33 shown in FIG. 1, and then a steel ball 34 was press-fitted into the filling hole 33 to seal it. Air of 1.5 kg/cm ² was sealed in the gas container 25. As a result of the operation test, an output proportional to external pressure was obtained in the range of 0-1.5Kg/ ^cm2 , and when the external pressure exceeded 1.5Kg/ ^cm2.
Even when the pressure increased to 10Kg/cm ² , the output of the water pressure detector 1 remained a constant value corresponding to 1.5Kg/cm ² . Note that the limit pressure value naturally varied slightly due to temperature changes, but since the limit pressure value is set higher than the upper limit of the measurement range, the slight variation does not pose a problem. Therefore, it was confirmed that the expected protection performance was achieved.

The effects of the present invention are listed below.

(1) An overpressure protection device that utilizes the compressibility of gas can be realized with a simple structure.

(2) Small and lightweight, suitable for low-cost mass production.

(3) Any protection lower limit _pressure can be easily set.

(4) Automatically restore normal pressure transmission function in response to overpressure removal.

(5) Since there are few moving parts and the amount of movement is small, high stability of operation and long life of the device can be expected.

(6) Overpressure protection can be provided without affecting the magnitude of fluid pressure acting on fluid pressure equipment.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of the overpressure protection device, and FIG. 2 is a diagram showing the relationship between the volume and pressure of the gas container. 1...Liquid pressure detector, 2...Overpressure protection device, 12
A...Pressure receiving surface, 20...Variable pressure chamber, 21...Housing, 211A...Pressure receiving surface of housing, 22
...protective diaphragm, 23...small chamber, 24...
Pore, 25... gas container, 30... expansion limiting wall,
d...Small gap, A...Gas, p _c ...Lower limit pressure for protection,
L...Enclosed liquid.

Claims (1)

[Claims] 1. A rigid housing defining a variable pressure chamber in contact with a pressure receiving surface of a fluid pressure device, a protective diaphragm fixed through a small gap from the pressure receiving surface of the housing to define a small chamber between the housing pressure receiving surface, and the above. A pore in the housing wall that communicates the small chamber with the variable pressure chamber, a flexible gas container containing gas at a protective lower limit disposed within the variable pressure chamber, the variable pressure chamber, the small chamber, and the pore. an expansion limiting wall that limits expansion of the gas container to keep the volume of the fluctuating pressure chamber constant when the pressure applied to the sealed liquid and the diaphragm does not exceed the protection lower limit pressure; An overpressure protection device for fluid pressure equipment, characterized in that the protective diaphragm is brought into close contact with the pressure receiving surface of the housing when an overpressure exceeding a protection lower limit pressure is applied.