What faults will happen to the diaphragm pressure gauge?

If the diaphragm pressure gauge fails during use, it will definitely have a great impact on our work, so everyone needs to attach great importance to it at any time to prevent us from knowing nothing after the failure. The following is an analysis of the failure of diaphragm pressure gauge introduced by Bian Xiao.

Gap pressure gauge switch is a small stop valve, which is mainly used to cut off the connection between gap pressure gauge and oil circuit. The switch plays a damping role, reducing the sudden jump of the gap pressure gauge and avoiding damage.

There are two ways to switch the pressure gauge, namely direct connection and indirect connection. The former pressure gauge is directly connected with the switch, and the latter is connected through a pipeline. It can also be divided into single-point type and multi-point type according to the number of tangents it can measure. Stop analyzing the following common faults of diaphragm pressure gauge switch.

(a) inaccurate pressure measurement.

There are usually damping holes on the switch of diaphragm pressure gauge. When the dirt in the oil regulates the damping too much, it will also cause the distant pressure gauge pointer to swing slowly, and the measured pressure value will be inaccurate. Therefore, attention should be paid to the adjustment of oil cleanliness and damping when using.

(2) Internal leakage increased.

After long-term use of KF pressure gauge switch, the valve port is too worn, closed seriously, and the internal leakage increases, which makes the pressure gauge pointer change with the pressure in the oil inlet chamber. The gap of K-type diaphragm pressure gauge switch increases due to the wear of sealing surface, which makes the pressure of each measuring point collude with each other. At this time, the worn parts should be replaced to ensure that the isolation pressure gauge switch is used under normal conditions. I believe that after reading the introduction of this article, if you use the diaphragm pressure gauge again, you will not ignore the key points.

The measuring principle of diaphragm pressure gauge is: diaphragm pressure gauge adopts indirect measuring structure, the diaphragm is deformed under the pressure of the measured medium, and the sealing liquid is compressed to form a pressure equivalent to P, which is transmitted to the pressure instrument to display the pressure value of the measured medium.

It is suitable for measuring the pressure of liquid, gas or granular solid medium with high viscosity, easy crystallization, high corrosiveness and high temperature. There are many kinds of materials for isolation film to adapt to various corrosive media.

Application differences:

Ordinary pressure gauges are used to measure the pressure of non-corrosive liquid gas;

Diaphragm pressure gauges are commonly used in two aspects: 1. Stop pressure measurement at the center with corrosion resistance, high viscosity and easy crystallization (the measured medium is corrosive, and different barrier data should be used for different corrosive media); 2. Food hygiene requirements, when measuring pressure with ordinary pressure gauge, because the measured medium does not move in the pressure gauge, it is easy to be polluted repeatedly.

The barrier is very fragile, so be careful during transportation and installation.

Application principle of pressure gauge

The selection of pressure gauge should be based on the production requirements of the use process, and the specific situation should be analyzed. On the premise of meeting the process requirements, it should be comprehensively considered in line with the principle of economy. Generally, the following aspects should be considered:

1. Selection of types

The selection of instrument type must meet the requirements of process production. For example, whether remote transmission, automatic recording or alarm is needed; Whether the properties of the measured medium (such as the temperature, viscosity, corrosiveness, dirtiness, flammability and explosion, etc.) put forward special requirements for the instrument, and the requirements of the field environmental conditions (such as humidity, temperature, magnetic field strength, vibration, etc.) for the instrument type, etc. Therefore, the correct selection of instrument type according to process requirements is an important prerequisite to ensure the normal operation and safe production of instruments.

For example, the spring tubes of ordinary pressure gauges are mostly made of copper alloy (alloy steel for high pressure), while the spring tubes of ammonia pressure gauges are all made of carbon steel (or stainless steel), and copper alloy is not allowed. Because ammonia reacts with copper and will explode, ordinary pressure gauges cannot be used to measure ammonia pressure.

The oxygen pressure gauge can be exactly the same as the ordinary pressure gauge in structure and material, but the oxygen pressure gauge must be oil-free. Because oil enters the oxygen system and easily causes explosion. When the oxygen pressure gauge is used for calibration, it can't use oil as the working medium like ordinary pressure gauges, and the oxygen pressure gauge should strictly avoid contact with oil stains during storage. If the existing pressure gauge with oil stain must be used to measure the oxygen pressure, it must be cleaned repeatedly with carbon tetrachloride before use and carefully checked until there is no oil stain.

2. Determination of measuring range

In order to ensure that the elastic element can work reliably in the safe range of elastic deformation, when selecting the range of pressure gauge, enough room must be left according to the measured pressure and the speed of pressure change. Therefore, the upper limit value of pressure gauge should be higher than the possible maximum pressure value in process production. According to the "Technical Regulations for Chemical Automatic Control Design", when measuring the stable pressure, the maximum working pressure should not exceed 2/3 of the upper measurement limit; When measuring the pulsating pressure, the maximum working pressure should not exceed 1/2 of the upper measurement limit; When measuring high pressure, the maximum working pressure should not exceed 3/5 of the upper measurement limit. Generally, the minimum value of the measured pressure should not be less than 1/3 of the upper limit value of instrument measurement. Thereby ensuring the linear relationship between the output of the instrument and the input quantity.

After calculating the upper and lower limits of the instrument according to the maximum and minimum values of the measured parameters, this value cannot be directly used as the measuring range of the instrument. When we choose the upper limit value of the scale of the instrument, we should choose it from the standard series stipulated by the state. The standard series of measuring range of pressure gauges in China are: -0.1-0.06,0.15; 0-1,1.6,2.5,4,6,10X10" MPa (where n is a natural integer and can be positive or negative).

3. Selection of accuracy grade

According to the maximum absolute error allowed in process production and the selected instrument range, the maximum allowable reference error of the instrument is calculated, and the precision of the instrument is determined in the precision grade specified by the state. Generally speaking, the more precise the instrument is, the more accurate and reliable the measurement result will be. However, it cannot be considered that the higher the accuracy of the selected instrument, the better, because the more precise instrument is generally more expensive, and the more troublesome it is to operate and maintain.

Choose examples:

1. When measuring special media such as viscosity or acid and alkali, diaphragm pressure gauge, stainless steel spring tube, stainless steel movement, stainless steel shell or bakelite shell should be selected.

According to the different measured media, there should be specified color code on the pressure gauge, and the name of special media should be indicated. The oxygen meter must be marked with the words "No oil" in red, with dark green color code for hydrogen, yellow color code for ammonia and so on.

2, when installed against the wall, should choose the edge of the pressure gauge; When directly installed on the pipeline, the pressure gauge without edge should be selected; When used to directly measure gas, a pressure gauge with a safety hole behind the case should be selected. For the sake of pressure measuring position and convenient observation and management, the diameter of the watch case should be selected.

According to the threaded joints and installation methods, the instruments in section 4.1.2 of the national standard for pressure gauges "General Pressure Gauges" GB/T1226-2001 are divided into direct installation pressure gauges, embedded (disc-mounted) pressure gauges and convex (wall-mounted) pressure gauges.

1, the installation position of the pressure gauge should meet the requirements of the installation state, the dial should not be placed horizontally, and the installation position should be convenient for the staff to observe.

2. The distance between the pressure gauge installation place and the pressure measuring point should be as short as possible, so as to ensure good sealing and no leakage.

3. There should be a buffer at the front end of the installed pressure gauge; In order to facilitate inspection, a cut-off valve should be installed under the instrument; When the medium is dirty or has pulse pressure, filters, buffers and stabilized gas can be used.

Link-B2B is a professional supplier listing service platform which will provide high quality and trustworthy supplier list to international buyers. If you are looking for pressure gauge  suppliers, feel free to visit Link-B2B.com and send a request.