The three-valve manifold consists of three valves that communicate with each other. According to the role of each valve in the system can be divided into: the left side of the high pressure valve, the right side of the low pressure valve, the middle of the balance valve. Three valve group and poor transmitter supporting the role of the positive and negative pressure measurement chamber and the pressure point conduction or open; or positive and negative pressure measurement chamber disconnected or conduction.
The main role: in the installation and removal of the time, need to use the balance valve. Otherwise, the differential pressure range is generally small, if the manufacturers overload capacity is not strong, it is easy to damage.
Give a simple example: If the differential pressure is 60KPa, the pipe pressure is 1MPa, if there is no balance valve, the three valve group whether the first positive pressure chamber or negative pressure chamber, will immediately lead to both sides of the differential pressure far more than the set value. Because the first side of the party will be directly connected with the atmosphere, the equivalent of 0.1MPa, this operation is fatal.
So what is the correct method of operation?
First, the differential pressure transmitter zero
(1) close the differential pressure transmitter positive and negative pressure chamber on the exhaust valve.
(2) the three valve sets on both sides of the positive and negative pressure valve closed (at this time the middle of the balance valve is turned on). See below:
Second, the flow measurement
The positive and negative pressure valves on both sides of the three valve sets are opened and the middle balance valve is closed to enter the measurement state (see figure below).