FAQ: To Fill Or Not To Fill a Swagelok Pressure Gauge?
by Jeff Hopkins, on 12/12/13, 8:00 AM
That is the question, and here are some tips to help you find the answer
Sometimes it's a good idea to use a liquid-filled pressure gauge. Sometimes it's better to use a dry gauge. The decision really depends on your specific application. Dry pressure gauges do fine in many applications, as long as they are installed in a location in your system where temperature fluctuations and vibration are minimal and flow of the pressurized medium is even and continuous. The leading cause of pressure gauge failure is vibration. In a dry pressure gauge, the sensitive internal components can be damaged by vibration and pressure spikes. Also, moisture and humidity can cause problems for dry pressure gauges. Just like your car windshield on a cold morning, condensation can fog up a dry pressure gauge making it difficult to read.
Four benefits of liquid filling
- The liquid absorbs vibration and pressure spikes.
- The dampening action of the liquid enables the operator to take an accurate reading during conditions of pressure oscillation and vibration.
- The liquid lubricates the interior moving parts of the pressure gauge, dramatically reducing the effects of wear and extending the lifespan of the pressure gauge.
- 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 the fill liquid
So if the pressure gauge you will be installing in your system will be exposed to excessive pressure or temperature fluctuations, vibration, or moisture, you might want to consider a liquid-filled pressure gauge. Swagelok offers several liquid-fillable pressure gauge models. with three standard flll liquid options: glycerin, low-temperature glycerin, and silicone oil. Other fluids are available through custom ordering. The choice of liquid type will depend on your system requirements. Be sure that the choice of fill liquid is compatible with your system in the rare chance that it leaks out of the gauge. Glycerin due to its higher viscosity is commonly used in room-temperature applications while silicone oil and low-temperature glycerin are often used in applications with temperature fluctuations 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.
An alternative to liquid filling
You may 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 to liquid filling is the use of 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 Swagelok Northern California, check out our Industrial and Process Swagelok Pressure Gauge catalogs page »
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