An air gage needs clean, dry, oil-free air at a steady pressure, delivered through a filter-regulator set just ahead of the gage. Feed it shop air of at least 60 psi, filter it to 5 µm, and hold the measuring pressure at 3 bar (43.5 psi); a 2-jet, single-channel plug uses about 0.88 SCFM (1.5 m³/h). Most "bad gage" calls we get turn out to be the air supply.
Why the air matters so much
An air gage measures size by measuring back-pressure. Air flows through a fixed restrictor to the jets, and the gap between the jets and the part sets the pressure the readout sees. Anything else that changes that pressure, a dip in shop air, a drop of water in a restrictor, a film of oil on a jet, shows up as a change in size. The gage can't tell the difference.
Air supply requirements at a glance
| Requirement | What you need | What goes wrong without it |
|---|---|---|
| Supply pressure | At least 60 psi at the gage, even when other equipment on the line is running | Readings drift or jump when a blow gun or cylinder on the same line fires |
| Regulated pressure | Two stages: a main regulator set to 60 psi, then a precision micro-regulator holding the measuring pressure at 3 bar (43.5 psi) | Span and zero shift; the gage won't hold its master |
| Filtration | 5 µm particle filter ahead of the gage | Dirt partly blocks restrictors and jets; readings go erratic |
| Dry air | No liquid water; drain filter bowls and drop legs | Water slugs cause sudden jumps and corrode tooling |
| Oil-free air | No lubricator on the gage line | Oil coats jets and restrictors and changes the reading |
| Air flow | About 0.88 SCFM (1.5 m³/h) for a 2-jet, single-channel plug while it is on; more jets and more channels use more | Undersized lines starve the gage when several run at once |
For comparison, Mahr specifies regular shop air of 40–125 psi for its Dimensionair dial gages, with an internal regulator holding the measuring pressure. If your plant runs near the bottom of that range, check that you still have 60 psi at the gage before switching to a digital readout.
How to plumb an air gage
- Take air from the top of the main line. Water collects at the bottom of pipes; a tee off the top keeps most of it out of the gage line.
- Add a drop leg with a drain below the takeoff, so water that does come down has somewhere to go.
- Don't share the gage line with heavy users. Blow guns, air cylinders and air tools cause pressure dips. Give the gage its own branch if you can.
- Install the filter-regulator close to the gage, and take its air from a point upstream of any lubricator on the shop system.
- Use the right hose and keep it short. Avoid kinks, long runs and loose push-in fittings; a leak between the regulator and the jets upsets the reading.
- Fit the right restrictor. On a Metro M5 display or MB-AG module, one restrictor set per air input matches the air circuit to your tooling.
The Air Gage Pro takes care of most of this: the filter-regulator and pressure gauge are built in, with a shop-air inlet on the back and quick-connects for your tooling on the front.
What to buy
| Your setup | What you need | Price |
|---|---|---|
| Air Gage Pro bench station | Nothing extra; filter-regulator and gauge are built in | Included |
| Metro M5 air display or MB-AG module | Precision filter-regulator (FIL-002), plus one restrictor set per input | $575 + $35 per input |
| Gages left on all shift | Air preparation set with air-saving: a valve shuts off flow between readings. Needs an MB-RO relay module ($285) and cable. | $950 |
Keeping the air clean
- Drain the filter bowl regularly, daily in humid weather or on wet systems.
- Replace filter elements on a schedule, not when the gage starts acting up.
- Check the gauge at the start of each shift, when you master. It should read 3 bar (43.5 psi). If it has moved, find out why before you reset it.
- Listen for leaks at hoses, fittings and O-rings.
More upkeep tips in air gage care and maintenance.
Air supply problems by symptom
| Symptom | Likely air cause | Fix |
|---|---|---|
| Reading drifts slowly through the shift | Supply pressure sagging toward the regulated setting | Check that supply stays at 60 psi or more under load; give the gage its own branch or a larger line |
| Reading jumps when other equipment runs | Shared line with blow guns or cylinders | Separate the gage line; raise supply pressure |
| Erratic, noisy readings | Water or dirt in restrictor or jets | Drain the bowl, replace the element, clean or replace the restrictor |
| Won't master or set span | Leak between regulator and jets, or blocked restrictor | Check hoses, fittings and O-rings; check the restrictor |
| Readings change after maintenance | Regulator setting moved | Reset the micro-regulator to 3 bar (43.5 psi), then master again |
If the air checks out, look at the masters, temperature and tooling next: 5 common reasons for incorrect air gage readings.
Quick answers
Can I run an air gage on plant air without a filter-regulator?
No. Unfiltered, unregulated shop air is the most common cause of bad air gage readings. Every standalone readout needs a filter-regulator ahead of it; the Air Gage Pro has one built in.
Can I use a lubricated air line?
No. Oil coats the jets and restrictors and changes the reading. Take the gage's air before any lubricator.
Can several gages share one filter-regulator?
Each gage should have its own, so one gage's flow doesn't change another's pressure. Several gages can share a well-sized supply line.
Do I have to master again after changing the air pressure?
Yes. Master again after any change to the regulator, air supply or restrictor.
Dimensionair and Mahr are trademarks of their owners, used only to identify compatible equipment.