Castair Liquid-Filled Pressure Gauge — 1/4" NPT, 2.5" Dial, 0-300 PSI, Back Mount (*GL251430B)
The *GL251430B is a liquid-filled 2.5-inch pressure gauge with a 1/4" NPT back-mount connection and a 0-300 PSI range. This is the gauge Castair uses on their own compressors where vibration, pulsation, or shock loading would cause a dry gauge to bounce and wear out the bourdon tube and movement prematurely. The liquid fill — typically glycerin — dampens needle movement, protects the internal mechanism, and lets you read the gauge accurately under running conditions. If you need to replace a gauge on a Castair compressor and the original was liquid-filled, this is the correct replacement.
Why Liquid-Filled vs. Dry Gauge?
On a running piston compressor, pressure pulses with every stroke. A dry gauge needle bounces with each pulse, which makes it hard to read and wears the pointer pivot and gear mechanism quickly. A liquid-filled gauge damps those pulses — the needle holds steady, you can read it at a glance, and the mechanism lasts years longer. Liquid-filled gauges also handle external vibration better, which matters on compressors mounted on rolling carts or vibrating floors.
The tradeoff: liquid-filled gauges cost slightly more, and if the casing cracks, the glycerin leaks. But on a compressor application with real pulsation, liquid-fill is the correct choice.
Gauge Specifications
- Fill: Liquid-filled (glycerin) — dampens vibration and pressure pulses for stable needle reading
- Connection: 1/4" NPT — standard for piston and rotary compressor pressure ports
- Mount: Back mount — pipe enters from the back of the gauge, face reads forward. Use when the gauge mounts to a panel, manifold, or tank fitting with the face pointing outward.
- Dial Size: 2.5 inches — readable from several feet away
- Range: 0-300 PSI — covers all Castair piston compressor operating pressures (95-175 PSI cut-out range) with substantial headroom
- Frame: Steel frame construction — durable for industrial shop environments
- Part Number: *GL251430B
Castair Gauge Lineup — Finding the Right Gauge for Your Application
Castair offers a full range of gauges. The model number encodes the specs:
Dry Gauges — Steel Frame
- G151860B — 1/8" NPT, 1.5" dial, 0-60 PSI, back mount
- G151860U — 1/8" NPT, 1.5" dial, 0-60 PSI, bottom mount
- G151816B — 1/8" NPT, 1.5" dial, 0-160 PSI, back mount
- G151816U — 1/8" NPT, 1.5" dial, 0-160 PSI, bottom mount
- G201420B — 1/4" NPT, 2" dial, 0-200 PSI, back mount
- G201420U — 1/4" NPT, 2" dial, 0-200 PSI, bottom mount
- G251430B — 1/4" NPT, 2.5" dial, 0-300 PSI, back mount
- G251430U — 1/4" NPT, 2.5" dial, 0-300 PSI, bottom mount
Liquid-Filled Gauges — Steel Frame
- *GL251430B — THIS PRODUCT — 1/4" NPT, 2.5" liquid-filled, 0-300 PSI, back mount
- *GL251430U — 1/4" NPT, 2.5" liquid-filled, 0-300 PSI, bottom mount
Flanged Dial Gauge
- GF251430B — 1/4" NPT, 2.5" flanged dial, 0-300 PSI, bottom mount
Back Mount vs. Bottom Mount — Which Do You Need?
Back mount (*GL251430B): The pipe fitting is on the back of the gauge body. The gauge mounts flat against a panel or manifold, face pointing toward the viewer. Use this when the gauge is mounting to a panel or tank port and you want a clean flush-mount look.
Bottom mount (*GL251430U): The pipe fitting is on the bottom of the gauge body. The gauge hangs or protrudes from a horizontal pipe or fitting, face pointing upward or outward. Use this for in-line pipe installations or when the fitting is below the gauge.
If you are replacing an existing gauge, note which direction the pipe enters — that tells you whether you need back or bottom mount.
What's in the Box
- 1 x Castair liquid-filled steel frame pressure gauge (*GL251430B)
- 1/4" NPT back-mount connection (male threads)
Technical Specifications
- Part Number: *GL251430B
- Connection Size: 1/4" NPT
- Mount: Back mount
- Dial Size: 2.5 inches
- Pressure Range: 0-300 PSI
- Fill: Liquid-filled
- Frame: Steel
- Application: Castair piston and rotary screw compressors, air receivers, pressure manifolds
Why Buy From Air Compressor Factory Direct?
We have supplied genuine Castair compressor parts and accessories since 2016. When you need to replace a gauge on a Castair unit, getting the factory part ensures the correct range, mount type, and dial size — a mismatched gauge is either unreadable or creates a fitting problem. We carry the full Castair gauge lineup and can help you confirm the right part for your compressor. Free shipping, free tech support at 866-217-0063, and the full Castair warranty.
Call 866-217-0063 for quick answers and help!
