How to use and pay attention to the piston pressure gauge

The piston pressure gauge is a measurement standard instrument that uses the principle of hydrostatic balance (that is, the fluid pressure acting on the effective area of ​​the piston is balanced with the gravity it loads) to measure pressure. It can transmit signals to instruments such as precision pressure gauges, pressure transmitters, differential pressure transmitters, pressure, pressure signal generators and digital pressure gauges. It has the characteristics of wide range, high precision, stable technical performance and easy use. It generally consists of a piston system, special weights, and a calibrator.

Common types of piston pressure gauges

According to the size of the effective area of ​​the piston, the action part of the force and the working medium, there are the following types of piston pressure gauges (Figure 1-18).

a. According to the working medium, it is divided into oil pressure type and gas type.

Commonly used working fluids for hydraulic types include transformer oil, medicinal castor oil, glycerin and ethylene glycol mixture, etc. Commonly used working gases include air, ammonia, etc.

b. Classified according to the structure of the piston and piston rod and the method of loading weights

Loaded piston pressure gauge, piston pressure gauge with booster, controllable gap piston pressure gauge, piston pressure gauge with balancing device.

Basic parameters of piston pressure gauge measurement performance

The basic parameters that affect the measurement performance of the piston pressure gauge include the effective area of ​​the piston, the descending speed of the piston and the duration of the piston rotation.

a. Effective area of ​​piston

The effective piston area is the instrument constant of the piston pressure gauge. Its value is the ratio of the combined force of the piston, load-bearing chassis and weight to the pressure at the bottom of the piston.

b. Piston falling speed

Under specified pressure, the speed at which the piston drops caused by fluid leaking from the piston clearance. If the rate of decline is too great, pressure measurement using a piston pressure gauge becomes impossible.

c. Piston rotation duration

Under the specified starting speed condition, the time during which the piston rotates freely is called the piston rotation duration. When using a piston pressure gauge, if the piston is stationary, there will be static friction to reduce the gravity of the weight; if the piston rotates freely, the piston and the piston barrel will move relative to each other, eliminating as much as possible the mechanical friction caused by direct contact between them, thereby Improve the accuracy of pressure measurement. Therefore, the piston should be given a certain amount of free time during operation.

The piston pressure gauge must indicate the nominal range and measuring range. If the lower limit of the measuring range cannot be determined, it shall be calculated as 10% of the upper limit of the measuring range.

The upper limit of the measurement range of the piston pressure gauge can be selected from 0.6mpa, 6mpa, 25mpa, 60mpa, 100mpa, 160mpa, 250mpa, and 500mpa. If it is inconsistent with the above range, you can select according to the latest value in the above range.

The basic parameters of the pressure gauge are shown in the table.

d. Conditions of use

Temperature: The operating temperature of the second-class pressure gauge is (20±2)℃; the operating temperature of the third-class pressure gauge is (20±5)℃. Relative humidity: below 80%.

How to use piston pressure gauge

a. The piston pressure gauge should be installed on a workbench that is easy to operate, firm and vibration-free. The tabletop should be made of strong and elastic material.

b. For newly purchased piston pressure gauges, the piston system, pressure pump, oil cup, and pipelines must be repeatedly cleaned with high-grade gasoline. After all the gasoline has evaporated, inject clean working medium into the calibrator and press with the hand wheel. Repeat several times until no bubbles leak out from the connection port between the calibrator and the piston. Then install the piston barrel on the calibrator. Use the hand wheel to pressurize the piston barrel until it is filled with medium, then coat the surface of the piston rod with working medium and insert it into the piston barrel to ensure that there is no air in the piston system.

c. The selection of the working medium of the pressure gauge is very important. The working medium should be selected with effective fluidity within the measuring range, small compression rate and no corrosion. Generally, transformer oil, a mixture of transformer oil and kerosene, and medicinal castor oil can be used. Before use, the kinematic viscosity and ph value of the medium must be measured, and it can be used only after meeting the requirements. See the calibration regulations for specific requirements.

d. The level of the piston pressure gauge must be adjusted before working. A specific method is: press with the hand wheel to raise the piston to the working position, place the bar level on the plane of the load-bearing rod tray, and rotate the piston to repeatedly adjust it to 0°, 45°, 90° and 135° on the horizontal plane. Meet the requirements. This actually requires that the plane of the load-bearing chassis be kept perpendicular to the center line of the piston, so that the gravity of the weight acts vertically on the effective area of ​​the piston. The non-verticality of the second and third grade piston pressure gauges must not exceed 5°.

e. Working position of piston pressure gauge

For piston pressure gauges without a limiter, the position where the piston is immersed in the piston barrel should be 2/4 to 3/4 of the full length of the piston; the piston with a limiter must not touch the limiter; with sliding bearings and ball bearings Pressure gauge, the indicator line that raises the piston to the working position is the working position of the piston pressure gauge.

f. When the piston is boosted to the required pressure value, the piston must rotate clockwise in the working position at an initial angular speed of 30 to 60 r/min, and be able to remain in the working position.

g. The special weight of the piston pressure gauge must be kept clean. Handle it with care when using it. When adding weights, be sure to ensure a tight fit between the weights. Otherwise, when the pressure gauge is working, the weight may easily be thrown out by rotating the piston, causing accidental injury to the operator or damage to the instrument.

h. The piston pressure gauge and the special weight must be used together as required, because the effective area of ​​the piston of the pressure gauge is different, and the quality of the matching special weight is also different.

i. When using a piston pressure gauge, the pressure should be increased and decreased slowly. If the pressure is increased or decreased rapidly, it will not only impact the piston, but also be dangerous.

Precautions for using piston pressure gauge

a. When the piston pressure gauge is not in use, it should be covered with a dust cover to prevent dust and foreign matter from falling on the pressure gauge.

b. When the operating temperature of the second and third grade pressure gauges exceeds (20±5)℃, temperature correction is required.

c. The working medium of the piston pressure gauge should be replaced every six months. At the same time, the rotation duration and descent speed of the piston of the pressure gauge should be verified. See the calibration regulations for specific requirements.

d. When using the piston pressure gauge, do not directly open the pressure relief valve when releasing pressure to prevent the weight from quickly moving down and breaking the piston rod. First, rotate the pressure lever in the opposite direction, and then open the pressure relief valve after the pressure is relieved.

e. The calibration cycle of piston pressure gauge is 2 years.