How to Select a Pressure Gauge

There are five primary items needed to properly select a pressure gauge:

1. Pressure Range – What pressure scale needs to be measured?
2. Dial Size – How large of a dial diameter is needed?
3. Connection Type – What size and orientation of connection is required?
4. Material – Should the wetted parts be brass or stainless steel?
5. Accuracy – What accuracy of measurement is required?

1. Pressure Range
What pressure scale needs to be measured?  Generally speaking the gauge pressure span should be double the normal operating pressure of the application it is used on.  In other words, if the normal pressure of the system is 150 psi, you should select a pressure gauge with a 300 psi range.  If a gauge with the exact range is not available, it is best to round up.  For example, if the normal system pressure is 100 psi and a 200 psi range is not available, it is preferable to round up to a 300 psi gauge.

 

2. Dial Size
How large of a dial diameter is needed?  Dial size is simply the diameter of the circular face of the pressure gauge.  When selecting a dial size, ease of reading and space available to mount the gauge are primary concerns.  Generally speaking, the larger the dial, the more expensive the pressure gauge.  The most common dial size is 2-1/2”.  Dial sizes can range from 1” up to 10”.
 

3. Connection Type
What size and orientation of connection is required?  The orientation of the connection refers to its location on the pressure gauge.  Choices of orientation are generally lower mount (protruding from the bottom of the gauge at the six o’clock position) or back mount (protruding from the rear of the pressure gauge).  The vast majority of pressure gauges are sold with male pipe thread connections ranging in size from 1/8” NPT to ½” NPT with ¼” NPT being by far the most common.
 


4. Material
Should the wetted parts be made of brass or stainless steel?  The wetted parts of the pressure gauge are the materials that come in contact with the fluid or gas being measured.  Stainless steel is more durable and more resistant to corrosion.  Brass is more economical.
 


5. Accuracy
What accuracy of measurement is required?  Pressure gauges are available with accuracies ranging from +/- 3/2/3% to +/- 0.1% of span.  The higher degree of accuracy required, the more expensive a gauge will be.  Common accuracies are 2-1/2%, 1%, and 0.5% of span.

Forberg Scientific Tech Support

If you are looking for pressure gauges please contact Forberg Scientific, Inc. customer service. Forberg can help with selecting a pressure gauge that will meet your application need.
Toll Free: 855-288-5330
Email: mechanicalsales@forberg.com

Advantages of Wika Liquid-filled Gauges

Liquid-filled gauges
Liquid-filled pressure gauges provide a number of advantages:

• The liquid absorbs vibration and pressure spikes
• The dampening action of the liquid enables the operator to
  take readings during conditions of rapid dynamic loading and
  vibration
• The liquid lubricates all moving elements, dramatically
  reducing wear in the movement
• Because most liquid-filled gauges are filled with non-aqueous
  liquid and hermetically sealed, they perform in corrosive environments
  and are immune to moisture penetration and icing
  and shock effects are lessened

Liquid-filled gauges enhance the reliability and integrity of the measuring system for long periods under extreme operating conditions.

Liquid-fill fluidAmbient Temperature Ratings (Table A)

Allowable operating range

Temperature range in which the operation of the gauge is not adversely affected by the filling liquid. At temperatures above the maximum rating, the fluid may break down. At temperatures below the minimum rating, the fluid may solidify (freeze).

Choose the right liquid

The type of liquid used to fill the gauge varies with the application. Although pure glycerine provides the best performance in most applications, each has its own requirements. Guidelines to help ensure that a fluid is properly matched to an application are:

• If icing is a problem, use gauges filled with silicone oil or other comparable liquids. They have low viscosities even at -60C
• If the system has electric accessories, such as contacts, use insulating oils
• If extreme temperature fluctuations are expected, use silicone oils

The higher the liquid viscosity, the greater its dampening capacity. The reason for this is that dampening changes in proportion to the temperature-dependent viscosity of the filling liquid. The suitable degree of dampening depends on the operating requirements the gauge must meet, such as pointer response time, pressure extremes, vibration and changes in pressure. WIKA can recommend specific liquids to suit problem applications.

Liquid-filled gauge case venting

For pressure gauges with full scale ranges of 300 psi and below (including vacuum and compound ranges of 30" Hg-0-200 psi and below), case venting (after the gauge is installed) is necessary to preserve the accuracy. Temperature fluctuations during shipment and in the process application cause the liquid filling to expand and contract which in turn increases or decreases case pressure. As a result, accuracy can be decreased and the pointer may not return to zero properly until the gauge is vented to the atmosphere.

To vent a WIKA gauge, move the valve to the open position which will release any pressure or vacuum built up in the case. If the gauge is installed in an upright position, the lever can be left in the open position. The lever allows the use of a gauge in a non-upright orientation.

If you would like to get more information about WIKA pressure gauges or other WIKA products please contace Forberg Scientific, Inc. customer service.
Toll Free: 1-855-288-5330
Email: mechanicalsales@forberg.com