The three-valve group is a pneumatic component used to control the flow cross-section of the pipeline. When the pressure of the gas source is constant, the gas pressurization rate through the needle valve increases with the increase of the flow cross section of the needle valve, so to a certain extent In the above, the needle valve is also an element that controls the gas pressurization speed.
In the manual control system and the pressure control system of the three-valve-magnet valve group, a needle valve with a large flow rate is generally used, because it is the main actuator in the control system, so the flow rate is required to be large, and the general diameter is When it is 1/2, but the flow rate of this needle valve is large, the control of the signal source is not sensitive (the signal source is generally a small flow), it can only be used to directly control the whirlpool surface. In the case of upper pressure, it is used as an actuator. If the needle valve is also used in the signal source, as shown in 19, 20, 21 in Figure 9-16, a needle with a higher sensitivity and a smaller flow rate is required. Shape valve (the integral needle valve in the QDZ proportional integral regulator is used in this system).
The installation of the three-valve group is relatively random. It can be installed horizontally or vertically. The sockets that are directly fixed to the output of the transmitter by four hexagon socket bolts can be directly connected to the pipeline. The three-valve group consists of a valve body, two shut-off valves and a balancing valve.
Operation procedure when the differential pressure transmitter is put into operation: First, open the two drain valves on the differential pressure transmitter, then open the balance valve, and then slowly open the two shut-off valves to remove the air or dirt in the pressure guiding tube. When the two drain valves are closed, the balance valve is closed and the transmitter can be put into operation. Differential pressure transmitter zero point online calibration operation procedure: first open the balance valve, close the two shut-off valves, you can zero-check the transmitter.
The three-valve is used in conjunction with conventional flanged differential pressure transmitters and can be mounted directly with long bolts and 3051CD with coplanar flanges. The three-valve type has three types: plate type (W type), flange type (T type) and flange-flange type (H type). The center distance of the DC three-valve instrument interface (outlet) is 54mm, which is directly connected to the high-low voltage interface of the differential pressure transmitter. The O-ring is pressed and sealed by bolts.
Two shut-off valves connected to the process end of the three-valve group are used to cut off the connection between the process fluid and the meter. A balance valve is used in the middle of the two shut-off valves to balance the high and low pressure chambers to facilitate the adjustment of the differential pressure transmitter. zero. Two bleed plugs (optional) between the meter interface and the two shutoff valves are used for blowdown and calibration purposes.