Blog posts tagged with 'pressure gauge'

So you’ve figured out what size dial and connection you need on the gauge for your application. You even know your preference on wetted materials. But what about having the gauge dry vs. liquid filled? What are the benefits to a liquid filled gauge? Are there any negatives? Believe it or not, determining this feature can be puzzling for many customers.  Be confused no more – Big Bear will explain everything you need to know about why a gauge is liquid filled.
To put it simply, liquid filling a pressure gauge is strictly used as an inexpensive way to steady the needle and lubricate the internals of a gauge during applications with vibration. The most common fill fluids used are Glycerin and Silicone. Glycerin is used in around 95% of all liquid filling applications and is typically the “standard.” The reason these fluids are used is because they’re more viscous and their thickness helps keep the needle steady. Some gauges come dry but can be filled simply by filling the hermetically sealed gauge case through the fill port (usually at the top) and then reinserting the fill plug when finished.
As with any decision making, you should outweigh your pros and cons when deciding what’s right for you. Let’s break that down for you here:
Benefits of a Liquid Filled Gauge

• It steadies the needle. Without liquid filling the gauge, the needle would bounce erratically making it difficult to pinpoint where the needle is exactly pointing on the gauge
• It’s an inexpensive solution and in many cases comes standard on a gauge
• It helps increase the life of the gauges by dampening as well as lubricating the mechanical parts of a pressure gauge

Negatives of a Liquid Filled Gauge

• Discoloration (darkening or yellowing) of glycerin over time due to exposure of UV rays or extreme temperature changes
• Standard Glycerin is really only good down to 20 degrees Fahrenheit. It is not recommended for cold environments
• Risk of leakage
• Pressure can build up in the case due to expansion and contraction of fluid from temperature changes (usually small, 1 PSI or so) affecting the accuracy of the reading as well as bring the needle off of zero

While some of these negatives can seem like deal breakers, there are easy solutions to these issues. We’ll start with discoloration. If potential discoloration is a concern, instead of choosing Glycerin, go with Silicone. Silicone has a bigger temperature tolerance and is not as easily affected by UV rays.  Because of this, Silicone tends to keep its color longer than Glycerin.

If your application has very low temperatures of 0 degrees or below, Silicone or a mixture of Glycerin and distilled water can be used instead of pure Glycerin. Both of these fluids will allow for lower temperatures down to -40 degrees Fahrenheit.

As for leakage, this is always a risk with liquid filled gauges but the risk is very low.  The chance of leakage depends on the quality of the gauge you’re using as well as the application. If your main concern is leakage, to decrease risk, use a crimped bezel type instead of a bayonet due to the crimped bezel holding the gasket in place permanently and is less likely to come loose in the field or by human error. Again, the risk of leakage is low nowadays due to improvements in manufacturing technologies and standards.

Last but not least, let’s talk about pressure build up. Pressure build up inside a gauge can happen and is very natural for a liquid filled gauge. The pressure build up (usually very minimal) can sometimes cause the needle to move off of zero and/or cause the gauge to read inaccurately + or – 2-4%.  To alleviate the pressure, burp the gauge by slightly lifting the fill plug. Once done, you’ll see the needle move back to zero.  If you’ve never done this before, we recommend watching Kodiak Controls' short video for a step by step guide on how to burp a pressure gauge.

If you have any further questions or would like help in finding what pressure gauge is right for you, contact us and our trusted staff will be happy assist.

A pressure gauge out of calibration can be extremely frustrating.  The gauge may constantly point off of zero when there’s no pressure in the line or the gauge is consistently reading 5% above or below the range it really should be reading based on your other instrumentation.

One solution to this problem is to utilize the adjustable pointer on the pressure gauge assuming your gauge has one.

Most industrial pressure gauges will have an adjustable pointer because gauges will commonly fall out of calibration out in the field due to vibration, pulses, or just general use.  Gauges that don’t typically have them are smaller utility pressure gauges or liquid filled gauges.  Usually they’re lower in cost and its cheaper just to replace than try and worry about adjustments.

Below is a link to a video by our friends at Kodiak Controls explaining how to adjust the calibration of a pressure gauge using an adjustable pointer.  Keep in mind that an adjustable pointer can only help if the needle is off by 1-10% of the full range.  So, if you have a 100 psi gauge and the needle is always off by 3 psi, an adjustable pointer will work great.  But, if your 100 psi gauge is off by 30 psi, an adjustable pointer is not your solution.  There is a bigger issue at hand and you may need to purchase a new pressure gauge.  Enjoy the video!

How to Use an Adjustable Pointer

On high vibration industrial applications, reading a pressure gauge can often be frustrating or in some cases down right impossible without the proper configuration on the gauge.  Very often, the end user may experience:

• The indicating needle shaking back forth making it difficult to get an actual reading
• The indicating falling off its access from the vibration
• Damage or short longevity of the gauge due to constant wear and tear of the pressure gauge internals

There are a few options that can be used to help legibility of the pressure gauge:

1. Liquid Filling – Liquid filling the gauge with either a glycerin or silicone is easily the most popular solution and least expensive.  The viscosity of glycerin or silicone makes it a thicker fluid than something water.  With the case filled with glycerin, the needle has a harder time from shaking back forth from the vibration.  This in turn steadies the needle and allows for accurate reading.  In addition to help steady the needle, the glycerin also acts as a lubricant for the internals of the pressure gauge allowing for a longer life out in the field.
2. Dampening Movement – Getting a pressure gauge with a dampening movement is the next best option especially for those who do not like liquid filling and prefer a dry gauge.  A silicone dampener is put on the internals of the pressure gauge near the axis of the pointer.  This steadies the pointer and allows for the same outcome as if the gauge was liquid filled.  Typically a dampening movement needs to be special requested though
3. Capillary Tubing with Diaphragm Seal – As an option for extreme vibrating applications where liquid filling and/or dampening movements aren’t enough, the pressure gauge is often mounted to a capillary tube and diaphragm seal filled system.  The diaphragm seal is mounted at the process connection.  Capillary tubing (often 5 feet in length) is connected to the diaphragm seal and on the other end of the tubing is the pressure gauge.  The pressure gauge is then typically mounted to a wall or panel away from the vibration and a proper reading can be seen.  The diaphragm seal, capillary, and gauge assembly is filled with a fluid (often silicone), to allow for an accurate reading.

For a complete list of our liquid filled gauge options, take a look at our mechanical gauges product page.

For differential pressure applications with caustic or thick medias, mounting a differential pressure gauge directly to the process can be detrimental to the integrity of the gauge.  The wetted material of the gauge may corrode away or the differential gauge could potentially become clogged.

A solution to this problem would be to isolate the wetted parts of a differential gauge by mounting diaphragm seals made of a compatible metal or plastic to the inlet and outlet sides of the differential gauge.  However, unlike a standard pressure gauge with one port, you cannot mount a diaphragm seal directly to the differential gauge because the ports of the gauge are typically too close together to accommodate the size of the diaphragm seal.

A solution to this is to install capillary tubing in between the gauge and the diaphragm seal.  This allows for flexibility during installation, safety from high temperatures or vibration, and room for the diaphragm seals to fit on the gauge.  The entire assembly is a filled system just like a standard gauge mounted on a diaphragm seal.  The air is evacuated from the assembly and replaced with a fluid (usually silicone or glycerin).
For more information on differential gauges and/or mounting instruments to diaphragm seals, contact us.

A pressure instrument by itself typically has a small orifice for the media to enter into it for measurement.  This works perfectly fine for applications such as water, air, or oil measurements.  But what do you do if the media has solids in it, is thick, and/or solidifies when it cools that can potentially clog the pressure instrument rendering it useless?
The answer is mount a diaphragm seal to the instruments.  A diaphragm seal is specifically designed to be a barrier between the media and the pressure instrument.  Pressure gauges, pressure transducers, and pressure switches can all be mounted to diaphragm seals (or gauge isolators as they’re sometimes called) through a “filling process” creating a sealed system between the instrument and the seal allowing for the utmost accuracy.
There are many kinds of diaphragm seals and all are used based on what fits best for the application.  Some types include:

• Mini Diaphragm Seals
• Large Diaphragm Seals
• Plastic Diaphragm Seals
• Flow-Through Diaphragm Seals

IMPORTANT: You cannot simply screw on a diaphragm seal to a pressure instrument.  As mentioned above, it needs to be a filled system.  Essentially the instrument is mounted to the diaphragm seal.  Then air is evacuated from inside the connection and replaced with a fill fluid such as glycerin, mineral oil, or silicone.  This allows for an accurate reading.
For more information on diaphragm seals or the mounting process, please contact us.