A valve manifold is a standard accessory for pressure transmitters and differential pressure transmitters. Providing a valve manifold in the instrument allows a calibration or change to the instrument without the necessity of plant shutdown. There are three types of valve manifolds: 2-way valve manifold, 3-way valve manifold, and 5-way valve manifold.
A 2-way valve manifold is used for pressure transmitters only. The typical 2-way valve manifold consists of 1 block valve and 1 drain or test valve. To calibrate the pressure transmitter, close the block valve and open the drain valve. Then connect the drain valve to the pressure generator to test the pressure.
A 3-way valve manifold is used for a differential pressure transmitter. The typical 3-way valve manifold consists of 2 block valves and 1 equalizer valve. To check the zero of the differential pressure transmitter, close the block valve and open the equalizing valve. The 3valve manifold is rarely used in the oil and gas industries—especially on offshore platforms—due to the absence of a test connection. Some manufacturers have modified the 3-valve manifold by providing a plugged test connection, but in general there is no test connection available.
Like the 3-way valve manifold, the 5-way valve manifold is also used for a differential pressure transmitter. The typical 5-way valve manifold consists of 2 block valves, 1 equalizer valve, and 2 vent or test valves. To check the zero of the transmitter, close the block valve and open the equalizing valve. To calibrate the transmitter for 3 or 5 point calibration, after the pressure is equalized, connect the test valve to a pressure generator. This 5-way valve manifold is the most common valve manifold for a differential pressure transmitter.
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