Does Your Swagelok Pressure Gauge Need a Fill-Up? Not Always

Here are some tips to help you decide between liquid-filled and dry gauges

When you shop for a pressure gauge, you have two basic choices: a liquid-filled gauge or a dry gauge. Which one is right for your job? The decision really depends on your specific application.

Dry and steady

Dry pressure gauges do fine in applications with minimal temperature fluctuations, minimal vibration, and an even and continuous flow of the pressurized medium. They need stable conditions because vibration is the leading cause of pressure gauge failure. The sensitive components inside a dry pressure gauge, can be damaged by vibration and pressure spikes.

Also, moisture and humidity can cause problems for dry pressure gauges. Condensation can fog up a dry pressure gauge, making it difficult to read.

Four benefits of liquid filling

Filling a pressure gauge with liquid alleviates the major drawbacks of a dry gauge.

1. The liquid absorbs vibration and pressure spikes.
2. The dampening action of the liquid lets the operator take an accurate reading even if pressure is oscillating, or if there is vibration in the system.
3. The liquid lubricates the moving parts inside the pressure gauge, dramatically reducing the effects of wear and extending the lifespan of the gauge.
4. Because most liquid-filled pressure gauges are filled with non-aqueous liquid and are hermetically sealed, they perform well in corrosive environments and prevent moisture penetration, fogging due to condensation, and icing.

Choosing a fill liquid

Swagelok offers several liquid-fillable pressure gauge models. They have three standard options for the fill liquid: glycerin, low-temperature glycerin, and silicone oil. Other fluids are available through custom ordering.

Once again, your specific system requirements will guide you toward the right choice of liquid type. Glycerin, due to its higher viscosity, is commonly used in room-temperature applications.  Silicone oil and low-temperature glycerin are often used in applications where temperature fluctuates or when icing is a problem. Also, for pressure gauges 60 psi and under, low-temperature glycerin or silicone oil is the better choice because the lower viscosity allows the gauge pointer to move through the liquid easier and respond quicker to system pressure changes.  

Whatever you choose, be sure that the fill liquid is compatible with your system in the rare chance that it leaks out of the gauge.

An alternative to liquid filling

Why not always use a liquid-filled pressure gauge? One reason is that you might not be able to justify the extra cost that goes along with liquid filling. Or, your system may not allow liquid-filled gauges. Yet you still want to minimize the effects of temperature and pressure fluctuations and vibration. A viable alternative is to use a dry gauge with snubber fittings, often referred to as dampeners. 

Swagelok snubber fittings protect gauges and other instruments from system pressure surges and shocks. Pressure damping (snubbing) is accomplished through the use of a porous sintered 316 stainless steel element. Installing a Swagelok snubber fitting upstream from the gauge reduces the gauge’s response rate. The response rate generally varies with the initial pressure drop across the porous element of the snubber fitting and allows the gauge to reach line pressure smoothly.

With five basic elements available, snubber fittings can meet the requirements of fluid applications ranging from light gases to liquids with viscosities above 1000 SUS (Saybolt universal seconds) (220 cSt [mm2/s]). Element designators are stamped on all fittings for proper identification.

Swagelok Pressure Gauges

For more details on Swagelok pressure gauges available from Edmonton Valve & Fitting, check out our online catalogue.

Additional Resources:

• Preventing Creep in Pressure Regulators
• FAQ Part 4: Answers from Your Edmonton Valve Represenatives
• Proactive Questions from September's Winterization Webinar (2012)