Liquid Filled vs Dry Pressure Gauges: Which Should You Choose?

The difference between a liquid filled pressure gauge and a dry one comes down to what is inside the case. A liquid filled gauge has its case filled with glycerine or silicone oil. That fill protects the movement from vibration and pulsation, lubricates the moving parts and slows corrosion. A dry gauge has an air-filled case and suits clean, stable, low-vibration duties at lower cost. This guide explains how each design works, when the extra cost of liquid filling pays off, and how to choose between them for pumps, compressors, hydraulics, steam and process lines.

How a pressure gauge works

Most mechanical gauges use a Bourdon tube. This is a curved, flattened metal tube that is sealed at one end and open to the process at the other. As pressure rises, the tube tries to straighten. That small movement is passed through a linkage and gear sector to a pointer on the dial. When pressure falls, the tube springs back.

The movement is delicate. Fast pressure changes and mechanical shaking can make the pointer flutter, wear the gears and shorten the life of the gauge. Liquid filling is the standard answer to that problem.

What is a dry pressure gauge?

A dry gauge has an empty case, so the movement sits in air. These gauges are simple, light and economical. They suit clean systems with steady pressure, such as a compressed air regulator in a workshop or a water line with a stable supply pump.

Dry gauges are also the right choice where filling liquid could cause contamination or safety problems. A well-known example is oxygen service, where gauges must be cleaned and kept free of oil and grease. In those cases the gauge must be specified for oxygen and should not be liquid filled.

The drawback is that a dry gauge offers no protection against vibration. The pointer can bounce, making it hard to read, and the internal parts wear faster in harsh duty.

What is a liquid filled pressure gauge?

A liquid filled gauge has a sealed case partly or completely filled with a stable liquid. The two common fills are:

• Glycerine: the usual fill for general industrial use. It damps vibration well and is widely used for hydraulic and pump applications.
• Silicone oil: chosen where temperature conditions are more demanding, because it stays fluid over a wide temperature range. Glycerine becomes more viscous in the cold, so silicone suits colder sites.

Always check the manufacturer’s stated temperature limits for the particular gauge and fill.

Benefits of liquid filling

1. Damps vibration and pulsation. The fluid absorbs shock, which steadies the pointer on pumps, compressors and engines.
2. Protects the movement. Lubrication reduces wear between the gears and bearings.
3. Reduces internal corrosion and condensation. With the movement immersed, moisture has less chance to form inside the case.
4. Improves readability. A calm pointer is easier to read quickly and accurately.
5. Extends service life. Less wear generally means a longer interval before replacement.

Liquid filled vs dry: side-by-side comparison

When to choose a liquid filled gauge

• Reciprocating or positive displacement pumps, where each stroke sends a pressure pulse.
• Compressors and engines that transmit strong vibration.
• Hydraulic systems with fast pressure changes.
• Mobile or portable equipment that is regularly knocked or shaken.
• Outdoor installations where moisture could condense inside a dry case.

When a dry gauge is the better option

• Clean compressed air or gas lines with steady pressure.
• Applications that forbid oil or glycerine contamination, including oxygen and some food and beverage uses.
• Budget-sensitive jobs where vibration is not an issue.
• Gauges that will be filled later on request, as some of our stainless steel models are supplied dry with liquid filling available.

What accuracy should you expect?

Accuracy for analogue gauges follows a class system. Under EN 837-1, accuracy classes include 0.6, 1.0, 1.6, 2.5 and 4.0, where the number is the permitted error as a percentage of the span. A class 2.5 gauge on a 0 to 1,000 kPa range may be wrong by up to 25 kPa at any point.

The gauges we stock illustrate typical values:

• L63 and L100 liquid filled gauges: ±2.5% of full scale
• AD-D-2 63 mm stainless steel gauge: ±1.6% of full scale
• AL-F-2 100 mm and AL-H-2 stainless steel gauges: ±1.0% of full scale
• Solfrunt 1981 solid front gauge: 0.5% of full scale

If you need better than around 0.5% or want data logging, consider a digital pressure gauge instead.

Our liquid filled and stainless steel gauges

The L63 and L100 are liquid filled gauges with a 304 stainless steel case, a brass Bourdon tube and connection, and a polycarbonate window. Both have a dual kPa and psi scale. The L63 has a 63 mm dial and a 1/4″ BSPT connection. The L100 has a 100 mm dial and a 3/8″ BSPT connection. Both cover ranges from -100/0 kPa to 0/4,000 kPa, with details on the datasheet.

For corrosive duty, the 316 stainless steel wetted parts of the AD-D-2 (63 mm), AL-F-2 (100 mm) and AL-H-2 (160 mm) suit more aggressive media. They are supplied dry, with liquid filling available on request. For surge protection in refinery-type duty, the Solfrunt 1981 has a solid front, full rear blowout protection and an optional high point indicator. For very low pressure air and gas, the KPCh capsule gauge reads from 0 to 2.5 kPa up to 0 to 60 kPa and is not suitable for liquids.

See every option in the pressure gauges category.

How to select a pressure gauge in six steps

1. Define the media. Is it air, water, oil, steam or a corrosive chemical? This sets the wetted material.
2. Set the range. Aim to keep steady pressure within about the middle to upper-middle of the scale, leaving headroom for spikes.
3. Pick the case size. 63 mm suits compact panels, 100 mm is the common industrial size, and 160 mm helps with distance reading.
4. Check the connection. Match BSPT, NPT or BSPP, and the thread size, to the port. Position can be lower mount or back mount.
5. Decide dry or filled. Use the table above.
6. Set the accuracy. Choose the class that matches the risk of a wrong reading.

Installation and maintenance tips

• Fit a snubber or restrictor if the pressure pulses sharply. Some of our gauges accept restrictors.
• For steam or hot media, use a pigtail siphon to protect the gauge. Our gauge datasheets recommend a pigtail above 60 degrees Celsius.
• Seal tapered threads with a suitable sealant and avoid over-tightening.
• Turn the gauge off the process before removing it, and release pressure first.
• Check for a vented fill cap where fitted, and follow manufacturer guidance on venting.
• Replace gauges that show a bent pointer, leaks or a pointer that does not return to zero.
• Calibrate periodically. See pressure gauge calibration.

Common problems and how to avoid them

A bouncing or fluttering pointer

This points to vibration or pressure pulsation. A liquid filled gauge helps, and a snubber or restrictor in the pressure port helps further by slowing the rate of change that reaches the Bourdon tube. Mounting the gauge on a short remote line instead of directly on a vibrating pump is another option.

A pointer that does not return to zero

The tube may have been overstressed by a pressure spike or by exceeding the range. Replace the gauge, because the damage affects every reading. To prevent a repeat, choose a range with more headroom and consider a gauge with a high point indicator or blowout protection.

Condensation inside a dry case

Outdoor dry gauges can fog on cool mornings. A liquid filled case leaves little room for moisture, which is one reason it is common on outdoor pump stations and mobile plant.

Cloudy or low fill

A gauge that has lost fill through a leak or a damaged seal should be taken out of service. Continuing to use it removes the protection the fill was meant to provide.

Choosing the wetted material

The material in contact with the process matters as much as the fill. Brass and copper alloy suit air, water and many oils. For corrosive media, or where food or hygiene concerns apply, choose stainless steel. The L63 and L100 use a copper alloy connection with a brass Bourdon tube, while the AD-D-2, AL-F-2 and AL-H-2 use 316 stainless steel for the tube and connection. Always check that the wetted parts are compatible with your fluid before you buy.

Frequently asked questions

Is a liquid filled gauge more accurate?

Not by itself. The fill improves stability and life, but accuracy depends on the gauge class and build quality.

Can I use a liquid filled gauge on a hydraulic line?

Yes, this is one of the most common uses, because the fill damps the pulses from the pump.

Why does my filled gauge have a small hole or vent?

Some gauges are supplied with a vent or a rubber plug to equalise case pressure with temperature changes. Follow the instructions for your model before installing.

Can I refill a gauge myself?

Refilling is best left to a qualified instrument technician, because the wrong fluid or an incomplete seal can damage the gauge.

What is the difference between a pressure gauge and a manometer?

A manometer traditionally measures pressure using a column of liquid, while a gauge uses a mechanical element or an electronic sensor. Our guide to the calibration of manometers covers that device.

Get help choosing

If you are not sure whether a dry or liquid filled gauge suits your site, send us your application details. Tell us the media, pressure range, temperature and connection, and we will point you to a suitable gauge from our shop.