1 Install the pressure source component
1.1 Installation Conditions
There are two types of pressure source components. One is the pressure nipple, which is a short tube. Used to weld pressure points and pressure valves on pipes. One is the external thread nipple, that is, one end has a external thread, generally KG1/2", and one end has no thread. After determining the pressure point on the pipeline, weld the unthreaded end to the pressure point on the pipeline (vertical opening), and screw the threaded end directly on the internal screw stop valve (primary valve). No matter which type of pressure is used, the installation of pressure source components must meet the following conditions:
1) The installation position of the pressure taking part should be selected in a place where the medium flow rate is stable.
2) When the pressure source component and the temperature source component are on the same pipe section, the pressure source component should be on the upstream side of the temperature source component.
3) When welding the pressure source part, it should be noted that the end should not exceed the inner wall of the process equipment or process pipeline.
4) When measuring the pressure of turbidity media such as dust, solid particles or sediment, the source component should be mounted upward at an Angle. The horizontal process pipe should be installed at an acute Angle along the flow beam.
5) When measuring the pressure of liquid, steam or condensable gas with a temperature higher than 60 ° C, the source component of the local installation pressure gauge should be equipped with a ring bend or U-shaped condensation bend. Figure (a) and (b);
6) When measuring the pressure of drastic fluctuations (such as the outlet pressure of pumps and compressors), the needle valve and buffer should be installed before the pressure instrument, and the damper should be added if necessary. Figure (c);
7) When measuring the pressure of the medium with large viscosity or easy crystallization, the isolation tank should be installed on the pressure taking device, so that the tank and the pressure guide tube are filled with the isolation liquid, and insulation measures can be taken if necessary. Figure (d);
8) When measuring the pressure of dusty media, it is best to install a dust collector after the pressure device, as shown in (e).
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1.2 Pressure tubes
1) The pressure guide tube for installing the pressure transmitter should be as short as possible and have as few elbows as possible.
2) Selection of pressure guide pipe and pipe diameter: local pressure gauge generally selects Φ18*3 or seamless steel pipe. Pressure gauge bending or condensation bending is preferred to use Φ18*3, and the pressure guide pipe is usually Φ14*2 seamless steel pipe. High-pressure pipelines with pressure higher than 22MPa should use Φ14*4 or Φ14*5 high-quality seamless steel pipes. On the pipeline with a pressure lower than 16MPa, the pressure guide pipe is sometimes used with Φ18*3, but it is difficult to form it once and is generally not used. For low-pressure or micro-pressure dust gas, 1" water gas pipe is often used as a pressure guide pipe.
3) When the pressure guide pipe is laid horizontally, it must have a certain slope. In general, maintain a slope of 1:10-1:2. In special cases, the slope can reach 1:50. When the medium in the pipe is gas, a liquid discharge device (usually a blowdown valve) should be installed at the lowest position of the pipe. When the medium in the pipe is liquid, an exhaust device is provided at the highest point of the pipeline (usually an exhaust valve is installed, and some gas collectors are installed).
1.3 Pressure measurement by isolation method
1) The pressure of corrosive and viscous media is measured by isolation method, which is divided into blowing method and flushing method. Blowing method is isolated and used to measure the pressure of corrosive media or suspension with solid particles. Flush isolation, suitable for viscous liquids and suspensions containing solid particles.
2) In the pipeline using the isolation method to measure the pressure, there should be a liquid discharge device at the lowest position of the pipeline. There are two ways to infuse the spacer. One is to use compressed air to lead to a special isolation liquid tank and inject it from the blowdown valve at the lowest part of the pipeline to facilitate the discharge of air in the pipeline until the top placement valve is filled. This method is especially suitable for the case where the transmitter is installed away from the pressure taking point. Another method is that when the transmitter is installed near the pressure point, the spacer is poured from the top wire of the isolation container. In order to easily drain the bubbles in the pipeline, the first method is better.
1.4 Gasket
The gasket of pressure gauge and pressure transmitter is usually made of tetrafluoroethylene gasket. For oil products, gaskets made of oil-resistant rubber asbestos sheets can also be used. Steam water, air, etc. are not corrosive media, gasket materials can be selected ordinary asbestos rubber sheet. Saturated steam and superheated steam using copper pad or graphite pad.
1.5 Installation Position
The installation position of the local pressure gauge must be easy to observe. The pressure gauge at the pump outlet must be installed in front of the outlet valve.
2 The pressure pipe is connected with the corresponding valve
2.1 Classification by valves and fittings
1) Pipe connection system mainly adopts sleeve valve and sleeve or pipe joint. It is characterized by high temperature resistance, good sealing performance, convenient loading and unloading, and no need for hot welding.
2) The pipe connection adopts external screw stop valve and pressure pad pipe joint, which is the common connection form of chemical industry.
3) The pipeline connection system adopts external screw stop valve, internal screw gate valve and pressure gasket pipe joint, which is the common connection form of oil refining system.
The above three methods can be used freely, but when conditions are available, as far as possible to use the form of card type connection.
2.2 Commonly used matching valves
1) The pressure instrument needs to install a primary valve.
2) If the flange is connected, the primary valve is generally a gate valve.
3) It is not a flange connection, and the primary valve is generally a needle globe valve; If the medium is easy to block, generally use a needle ball valve; In the case of high temperature and high pressure, a valve should be welded with high temperature resistant material. The second way valve and the blowdown valve are usually J23W-160 needle valve, and the pressure grade and material are selected according to the field working conditions.
3 Installation of pressure instruments
The pressure opening on the horizontal pipe is generally drawn from the top or side for easy installation. When the pressure transmitter is installed and the pressure guide tube is drawn away, the bearing requirements for taking pressure on the horizontal and inclined pipelines are as follows: When the fluid is liquid, do not take pressure at the bottom of the pipeline at an Angle of 45° between the lower part of the pipeline and the horizontal center of the pipeline; When the fluid is steam or gas, it is generally the upper half of the pipeline, and the horizontal center line of the pipeline is within the Angle range of 0 to 45°.
Commonly used pressure gauge measuring pipeline connection see figure (a) ~ (e) above.
The installation method of the pressure transmitter is basically the same, which is divided into several ways, such as bracket installation, incubator and protection box installation, direct installation and so on. The bracket installation is divided into two types, one is the bracket on the wall, and the other is the bracket on the ground. These two elevations are generally :+1.20 meters ~+1.50 meters, keep the elevation of the transmitter indicator :+ 1.50 meters. If the two installation methods are in the same workshop or the same workshop, the elevation is required to be consistent, and the transmitters installed on the wall and on the ground (including differential pressure transmitters, etc.) should be consistent.