Overview of Pressure Gauge

It is important to consider the various information outlined to ensure appropriate pressure gauge selection and usage. Improper application can lead to instrument failure and possible personal injury and/or property damage. The following information is meant to be the overview of pressure gauge.

Types of Pressure Gauges

Winters offer a full range of pressure gauges suitable for virtually all types of applications. Some specific types of pressure gauges that will be covered in this manual are general-purpose Bourdon tube, capsule-type, duplex, and differential pressure gauges.

General-Purpose Bourdon Tube Gauge
This common type of gauge utilizes a C-Bourdon tube, which usually has an arc of 250 degrees. The process pressure is connected to the fixed socket end of the tube, while the tip end is sealed. Because of the difference between inside and outside radii, the Bourdon tube tends to straighten when pressure is applied. The non-linear motion at the tip of the Bourdon tube is converted to linear rotational pointer response through the use of gears and pinion movement. This type of pressure gauge is used in medium to high-pressure measurements with accuracies of 0.1 to 3% of full span. The pressure range capabilities starts from 15 psi (100 kPa) to 20,000 psi (137.8 Mpa).

Capsule-Type Gauge
Capsule-type are formed from welding two pre-formed plates together. Input process pressures cause the capsule to expand or contract which is then translated into a linear rotational pointer response through the use of gears and pinions. Bellows gauges are typically used in low to intermediate and vacuum pressure ranges with 0.1 to 1% of full span accuracy. Winters Instruments capsule gauges have pressure ranges from 0-15" H2O (0-3.7 kPa) to 0-10 psi (0-68.9 kPa).

Duplex Gauge
A Duplex gauge indicates two related pressures in a process. There are two Bourdon tubes inside the gauge casing which results in two separate readings. The principal of the operation is as described in the General-Purpose Bourdon Tube Gauge section for Winters' Duplex Gauges.

Tire Pressure Gauge
There are 3 basic types of tire pressure gauges (also called tire gauges). The dial tire pressure gauges, digital tire pressure gauges, and stick gauges. The gauges may look different, and display results differently, but all use the same principal. When the gauge is pressed onto the stem of a wheel, the air pressure in the tire pushes against some type of plunger which in turn actuates the readout section of the gauge assembly. Then we describe the similarities and differences between the different types of gauges.

Differential Gauges
The purpose of a differential gauge is similar to a duplex gauge, but this gauge will indicate the difference between two related pressures. Winters Instruments provide three different types of differential gauges; parallel Bourdon tube, magnet and piston, and opposing Bourdon tube designs.

Parallel Bourdon Tube Differential Gauge
The placement of the Bourdon tubes is similar to that of the duplex gauges. The gears and pinions are calibrated to measure the difference between the flex of the two Bourdon tubes and this is translated to a single pointer. This type of differential gauge is used when the indicating scale is 2/3 of the process static pressure due to the limitations of the Bourdon tubes.

Piston Differential Gauge
The sensing element is a spring-biased diaphragm, which moves linearly in proportion to the difference between two basic pressures. A magnet on the HI pressure side of the piston assembly moves with the diaphragm and rotates a follower magnet located adjacent to the pressure cavity. The gauge pointer is located at the end of the rotary magnet shaft and rotates with the magnet to provide gauge readings proportional to the differential pressures. This type of instrument can indicate small values of differential pressure even when used in high-pressure processes.
Return to Top.

Pressure Range

Select a pressure gauge with a full-scale pressure range of approximately twice the normal operating pressure. For Bourdon tube gauges, the maximum operating pressure should not exceed 75% of the full-scale range. The exception to this rule is the opposing Bourdon tube differential gauge. Failure to select a gauge within these criteria may result in premature fatigue and failure of the Bourdon tube.

Temperatures

The normal ambient temperature ranges are -40C to 70C (-40F to 158F) for dry gauges and -25C to 65C (-13F to 149F) for glycerin filled gauges. The process temperature for dry gauges can be up to 400C (752F). In situations where the process temperature is extreme, utilizing a syphon or remote mounting the pressure gauge with a capillary and diaphragm seal are reasonable alternatives.In general, a gauge is unduly hot if it cannot be grasped by hand without discomfort. It should be noted that gauges used on water might burst if exposed to frost. Please consult Winters for your specific requirements.

Materials

Winters provide a full range of casing and wetted parts to accommodate all types of applications. The most common wetted parts used are brass and 316 stainless steel. Brass wetted parts are suitable for use on the following types of media; air; oil, water and other non-corrosive fluids. For corrosive fluids, stainless steel should be specified. For special applications, other materials such as Monel can be used as well. Diaphragm seals may also be considered. Please consult Winters Instruments for assistance.

Vibrations

Vibrations and extreme ambient temperatures can affect the dial reading of the pressure gauges. These areas should be avoided as much as possible. Vibration effects can be minimized by the use of a dampening liquid such as glycerin or silicone. If vibration is extreme, then a flexible tube connected to an appropriate diaphragm seal should be considered.

Pulsations

If pressures are expected to pulsate violently, oscillate with high frequency or occur with sudden shock, a snubber should be considered. Winters snubbers incorporate sintered porous 316 stainless steel snubbing element with a large surface area to ensure long term effectiveness on most pressure media. Snubbers are available in the three viscosity classifications; heavy oil, water and air. Brass, stainless steel or Monel housing can be specified depending upon the media used.

Isolating Valves

It is recommended that isolating valves be fitted with the gauge. This enables the gauge to be removed at any time for checking, recalibration or replacing without interruption to the process. The valves should be opened or closed slowly to avoid sudden changes to pressure being applied to the gauge. It is recommended for systems that have an abrupt pressure surge at start-up to close the valves during initial start-up.

Installation Pressure Gauge

Location
Vibrations and extreme ambient temperatures can affect the dial reading of the pressure gauge. These areas should be avoided as much as possible. Vibration effects can be minimized by the use of a dampening liquid such as glycerin or silicone. If vibration is extreme, then a diaphragm seal connection should be considered.

Mounting
A suitable thread sealant is required for N.P.T. threads such as pipe dope or Teflon tape. Never use any part of the pressure gauge other than the wrench flats that is on the gauge socket. Always tighten with an open end or adjustable wrench on the wrench flats. Failure to do so will severely damage the pressure gauge. Please note the following special requirements for the piston differential gauge.

Piston Differential Gauge
Check instrument & identify HI and LO markings. HI identifies the high-pressure port; LO the low pressure port. If the instrument is installed backwards, it will neither operate nor be damaged.
It is recommended that the instrument be located above the pressure source to allow for drainage of the unit. Please note that since there is a magnetic movement, the piston differential gauge should never be mounted in direct contact with a steel surface. Failure to do so will cause a calibration
shift. Mount the gauge so that the gauge body is at least 1" (25.4 mm) away from metal surface with non-magnetic spacers or an aluminum-mounting bracket.

Venting Procedures
Due to pressure ¡°build up¡±, some gauges (usually lower pressure ranges such as vacuum, up to 100 psi) may reflect a reading that is slightly ¡°off zero¡±. To properly ¡°vent¡± the pressure gauge, please cut off tip of fill plug after you have installed the instrument.
Return to Top

Operation & Maintenance of Pressure Gauge

Storage
All pressure gauges should be placed in dry storage under ambient room temperatures. It is recommended to store the pressure gauges in their original packing boxes.

Inspection Frequency
Winters pressure gauges are rugged instruments featuring simplicity of design to provide dependable and efficient service. The frequency of inspection is dependent on the severity of service and how critical the accuracy of the indicating pressure is. The inspection frequency can range from monthly to annually basis.
Return to Top

Recalibration / Assembly & Disassembly Procedures

Positive Pressure Gauge
Inspect the pressure gauge for "zero reading" when there is no applied pressure. In many cases, the gauge pointer can simply be adjusted and then the gauge will work within specifications. However, if the gauge requires calibration, then follow the outlines procedures below.

Remove the ring and lens
Slowly pressurize the gauge to its full scale and slowly release the pressure back down to zero.
Check the gauge at a minimum of four equal pressure intervals against a Certified Test Gauge.
Adjust the movement accordingly by removing the pointer with a pointer extractor. Be careful not to bend the pointer shaft.
Removing the dial plate by loosening the holding screws.
When adjustments are complete, replace the dial plate and pointer.
Re-check the gauge for accuracy.
Check lens assembly gasket for any deformation, tears or cracks. If there are any visual defects, the gasket will need to be replaced.
Re-assemble the lens assembly.

Capsule-Type Pressure Gauge
The same inspection procedure applies as per the positive pressure gauge section above. The micrometer adjustable pointer is accessible by removing the white plastic knob on the lens and adjusting the screw. This is done without having to remove the lens. If calibration is required, please follow the outlined procedure below.
Remove lens by prying open the lens window with the notches provided on the sides of the case.
Slowly pressurize the gauge to its full scale and slowly release the pressure back down to zero.
Check the gauge at a minimum of four equal pressure intervals against a Certified.

Test Gauge

Adjust the movement accordingly by removing the pointer with a pointer extractor. Be careful not to bend the pointer shaft.
Remove the dial plate by loosening the holding screws.
When adjustments are complete, replace the dial plate and pointer.
Re-check the gauge for accuracy.
Replace the lens window.
Piston Pressure Gauge.
Other than replacing broken lens, there is only one area where the gauge may need attention. Erratic pointer action may indicate that cleaning is required. Calibration is not required. However, if the range spring is damaged or a new dial is required, the gauge should be returned to the factory for parts and recalibration.

For cleaning

Remove the low pressure end cap with 1" (25.4 mm) spanner wrench.
Remove the range spring and the spacers at the bottom of the spring pocket. BE CAREFUL NOT TO LOSE STACKING SPACERS, IF ANY
Remove the four ?-20 socket head screws and separate the body parts .
Remove the diaphragm assembly .
To replace the diaphragm, remove the screw at the top of the diaphragm disc to separate the assembly. DO NOT REMOVE THE SCREW IN THE MAGNET ASSEMBLY.
Clean parts in a solvent solution after removing the "O"-ring seals since solvents will attack the seal material
Place diaphragm disc on magnet shaft with "O"-ring groove facing away from magnet. Place new diaphragm over shaft with the open end of the convolution facing the magnet. Place the second disc over diaphragm so that centre "O"-ring groove faces diaphragm "O"-ring .
Replace the spring cup, and the #8-32 assembly screw. Tighten to finish assembly .
Place the diaphragm assembly back into the diaphragm pocket with the magnet end of the assembly at the high pressure side
Reassemble both body parts with the four ?-20 socket head screw .
Insert the spacers and the range spring into the spring pocket of the end cap. While holding the instrument with the low pressure port down, insert the end cap back into the low pressure side of the body .
Tighten the LO end cap and the instrument is now ready for service .
No recalibration is required.

For replacing the lens:

To replace a broken lens, check to see if the lens is held on by a bezel or snap-ring. To remove a bezel, which is a pressed on cover, either twist off by hand or pry off with a screwdriver. To remove a snap-ring, pry out the ring with a small screwdriver. Remove all glass chips, insert new lens and re-insert the bezel or snap. With snap-rings, locate the ring joint at the bottom of the gauge.

For replacing the pointer:

Remove bezel or snap-ring as previously described and clean out glass chips. Remove old pointer with pointer extractor or two small screwdrivers opposite each other under pointer hub. Pry off evenly being careful not to bend the pointer shaft. Install new pointer on zero. NOTE: Gauges with a zero peg must have the pointer set at a reference pressure (preferable mid-scale) to offset the preload against the zero pegs. Re-install the lens, as described under lens replacement.

Relative Articles:

Article Summary

Overview of Pressure Gauges,such as types of pressure gauges,installation pressure gauge,piston differential gauge,operation and maintenance of pressure gauge and so on.

Keywords

Pressure Gauge, Tire Gauge, Dial Tire Pressure Gauge

Sponsored Links

Relative Company

Relative Product