Useful information

Selection.

The notes below are intended to assist in the selection of pressure gauges. For complete and definitive information we recommend reference to BS837-2. If in doubt contact us.

Pressure Element
Three types of pressure element are commonly used in pressure gauges: Bourdon tube (most common), diaphragm and capsule. The one selected is normally dependent upon pressure range of the gauge. Generally the ranges are:
Bourdon tube: 0.6 bar to 1600bar.
Diaphragm: 2.5 mbar to 25 bar.
Capsule: Capsule 1 mbar to 600 mbar.

Pressure Range
The maximum working pressure of general industrial gauges should not exceed 75% of the full scale value when the pressure is steady and 65% when the pressure is cyclic. Airedale Instruments can supply special specification gauges to use a higher percentage of the scale or where occasional overpressure occurs. Alternatively an over-range protector can be fitted. Contact us for details.

Safety Design of Case
The level of safety design incorporated into the case is dependant upon the application of the gauge. If the pressure medium is gas or steam and the gauge range is above 25 bar, it must be of the safety pattern type.
Oxygen and acetylene gauges must be full safety pattern.
Capsule and diaphragm gauges are not recommended for oxygen and acetylene use.
Table 2 of BSEN837-2 gives full guidance on safety design criteria.

Materials
The material of the pressure sensing element, case and other components of the gauge must be suitable for the process fluid and application environment. It is important that the purchaser indicates to the supplier all information concerning the application to ensure suitable materials are selected.
If no standard materials are suitable it will be necessary to interpose a separator between the process fluid and the gauge. These can be supplied by Airedale Instruments, see pressure gauge products page, chemical seals, or contact us.

Other Criteria for Selection
Consult us if the application subjects the gauge to vibration, pressure pulsation, high or low temperature fluids and/or environment, shock loading, viscous or aggressive process fluids, solids in suspension, or a hostile environment.
If the gauge is to be used at an angle other than upright or a static head is present special calibration corrections will be required.
If the gauge is to be used on oxygen it must be oil free and of full safety pattern type.
It is important that the purchaser informs the supplier of any environment and process fluid factors relevant to the use of the instrument.

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Installation

The notes below are intended to assist in the installation of pressure gauges. For complete and definitive information we recommend reference to BS837-2. If in doubt contact us.

General Notes
Ensure the correct instrument for the application has been selected. If in doubt contact us.
Isolation valves are recommended to enable easy removal for calibration or maintenance.

Sealing of the Pressure Connection
A leak tight connection is essential. Gauges with parallel threads should seal on the bottom face and not on the thread. Ensure the seal is compatible with the process fluid. Gauges with taper threads are usually sealed using a jointing material or tape. This must be compatible with the process fluid.
Figure 1 of BSEN837-2 shows the correct methods of making pressure connections.

Vibration
Vibration of the gauge must be avoided as this causes excessive wear and difficulty in reading the dial.
If vibration is likely to be transmitted through the connecting pipe mount the gauge rigidly with a back flange or support bracket and use a flexible pipe to the gauge. A liquid filled gauge will reduce the vibration problem greatly.

Pressure Pulsation
As with vibration, pressure pulsations of the process fluid causes excessive wear and difficulty in reading the dial e.g. when the gauge is mounted on a pump. Depending on its magnitude an in line damper, glycerine filling or internal damped movement can solve the problem. Contact us for details.

Fitting the Gauge
Always use a spanner on the flats of the shank when connecting the gauge. Do not tighten by using the case. This can damage the gauge, effecting its safety and accuracy. Check the connection is leak tight when first applying pressure.
Unless marked on the dial or made to an agreed special specification the gauge should be mounted with the dial vertical.
Blowout backs or blowout devices should not be prevented from operating. Maintain a minimum distance of 20 mm from any obstruction to enable the blowout to operate.

Fluid Temperature
Excessive temperature should be avoided. If hot fluids are likely to enter the gauge a siphon or cooling coil must be fitted. Contact us for details.
Fluid inside the pressure element must not be allowed to freeze.

Static Head
If a liquid column (static head) is acting on the gauge the calibration needs to be corrected to allow for this.

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Pressure Gauge Safety and Maintenance

Inspection and Testing
Regular inspection and calibration is essential to maintain safety and quality.
The calibration and correct operation of pressure measuring instruments should be tested periodically. Testing should only be done by competent personnel. The equipment used must be suitable for the job and in a known state of calibration. Contact us for the supply of test equipment. BS EN837 gives guidance on the selection of suitable test equipment.
Airedale Instruments offer a repair and calibration service. Contact us for details and prices.

Abnormal Operating
Any pressure instrument which appears to be operating abnormally should be withdrawn from service, tested and calibrated.

Pressure Surges
When using pressure gauges sudden and violent surges of the pressure fluid must not be allowed to enter the gauge. Isolating valves should be opened slowly.

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Details of British and European Standards for Pressure Gauges

BS EN 837-1 Bourdon tube pressure gauges. - Dimensions, metrology, requirements and testing.

BS EN 837-2 Selection and installation recommendations for pressure gauges.

BS EN 837-3 Diaphragm and capsule pressure gauges - Dimensions, metrology, requirements and testing.

Please note! All the information above is given as a guide. We cannot be held responsible for any subsequent losses that may occur. Please refer to relevant British or International standards for confirmation.

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