Valve Manifolds for Instrument Connections: 2-Valve, 3-Valve, and 5-Valve

Instrument manifolds isolate and equalize pressure transmitters, differential pressure (DP) instruments, and gauges from the process. Standard 2-valve, 3-valve, and 5-valve manifolds serve different measurement configurations.

2-Valve Manifold

A 2-valve manifold consists of one isolate (block) valve and one bleed/vent valve. It isolates a pressure transmitter or gauge from the process for maintenance or calibration and bleeds trapped pressure safely before disconnection.

3-Valve Manifold

Used with differential pressure transmitters, the 3-valve manifold has two isolate valves (high pressure and low pressure sides) and one equalize valve. The equalize valve connects both sides of the DP transmitter to allow zeroing and prevent over-ranging during startup.

Startup sequence: open equalize, open both isolates, close equalizeShutdown sequence: open equalize first to equalize DP cell, then close isolatesNever close both isolates before opening equalize—DP transmitter may be damaged

5-Valve Manifold

The 5-valve manifold adds two bleed valves to the 3-valve design, allowing individual side venting and drain. This is preferred for applications where trapped liquid or gas pockets affect zero stability or where process fluid must be safely released before instrument removal.

Material Selection

Body: 316 SS for general process, Monel for HF acid, Alloy 20 for sulfuric acidSeats: PTFE for general service, Grafoil for high-temperature steamConnections: NPT or socket weld—choose to match instrument and impulse line connectionsPressure class: select manifold rated above maximum process pressure plus any potential surge

Maintenance

Valve seats in manifolds are small and susceptible to particle contamination. Flush instrument impulse lines before connecting to manifolds. Inspect bleed valves for leakage at each planned outage—bleed valve leakage can cause incorrect instrument readings.