Every pressure transmitter on your site sits behind a manifold, and that manifold decides how safely and easily your techs can isolate, vent, zero and calibrate the instrument. Order the wrong one and you're either missing a valve you need or fighting with extra ones you don't. Here's how I walk people through the choice.
2-Valve Manifolds: Isolate and Bleed
A 2-valve manifold has one block valve and one bleed (vent) valve. It's built for a single pressure connection: a gauge pressure transmitter, a pressure switch or a gauge.
Close the block valve to isolate the instrument from the process, then open the bleed valve to relieve trapped pressure before you work on it. Simple, compact, and all most static pressure points need.
3-Valve Manifolds: The Standard for Differential Pressure
A differential pressure (DP) transmitter has a high side and a low side, so it needs two block valves. The third valve is the equalizer, which connects the high and low sides together.
The equalizer lets you zero the transmitter at line pressure, and it protects the sensing element from seeing full pressure on one side only. On flow, level and filter DP applications, a 3-valve manifold is the usual starting point.
5-Valve Manifolds: More Control for Calibration and Critical Service
A 5-valve manifold adds valves for venting and testing. A common layout has two block valves, two equalizer valves with a vent or test port between them, which gives you a double block between the high and low sides.
That extra isolation matters in services where you don't want process leaking across from high side to low side, such as natural gas metering. It also lets a tech connect calibration equipment and vent the instrument without breaking the process connections. If your techs calibrate in place often, a 5-valve is usually worth it.
Mounting Style Matters as Much as Valve Count
Before you order, check how the manifold connects on each end:
- Flange-to-flange: bolts directly to a coplanar-style transmitter on one side and a flanged process connection on the other.
- Flange-to-pipe (direct mount): bolts to the transmitter and takes threaded or tube-fitting impulse lines on the process side.
- Pipe-to-pipe (remote mount): threaded or tube connections on both ends, mounted on a bracket or stand.
Also confirm body material (316 stainless is the common choice), pressure rating at your operating temperature, packing material, and the end connections your impulse tubing uses. Matching the manifold to your tube fittings saves an adapter and two extra leak points.
Follow the Sequence Every Time
Most manifold problems I've seen weren't the hardware. They were valves opened or closed in the wrong order, which can over-range or damage a DP cell. Write the sequence for putting the transmitter in service and taking it out of service into your site procedure, follow the transmitter manufacturer's instructions, and make sure every tech on the crew knows it. Our free Safety training course is a good place to start that conversation with your team.
Need Help Picking One?
A-Best Industrial Inc. Fittings, Valves, and Tubing is an authorized DK-Lok distributor, and we can help you match manifolds, needle valves, tube fittings and tubing for your instrument hookups. Tell us the transmitter model, the process and the pressure, and we'll help you get it right the first time.
Call us at 310-833-3353 or email sales@abesttube.com. We're open Monday–Friday, 8:00 AM–5:00 PM Pacific, with after-hours emergency service.