Notes for the Selection and Installation of Pressure Gauges

 

For your Guidance

These notes have been prepared to assist in the selection and installation of pressure gauges
for the purpose of ensuring as far as possible that the pressure gauges give satisfactory
service on the application for which they are intended and to ensure the highest possible
level of safety. For further information, reference should be made to A.S. 1349 1986, on which
these Notes are largely based.

 

Materials

The most usual wetted parts used in the construction of these gauges are made from brass
and bronze and similar non-ferrous materials e.g. Stainless Steel should be specified. 
For special applications e.g. when the pressure medium may solidify in the tube or may contain
solids in suspension, alternative designs or pressure gauges such as a diaphragm or a chemical
seal type should be used.

 

Environmental conditions should be taken into account when considering suitable materials for
Case etc.  Stainless Steel, weatherproof cases are available for corrosive atmospheres and
outdoor application.

 

Safety on Steam and Gas Pressure Measurement

For certain steam and gas applications, safety pattern gauges MUST be used and these must
incorporate a solid baffle between dial and pressure element, a splinter-proof or clear plastic window
and blow-out release.  Surface mounting gauges with a blow-out release at the back, MUST be
mounted at least 20mm away from the surface panel by means of distance pieces.  For oxygen,
safety pattern gauges MUST be used, MUST be supplied degreased and kept free from oil contamination. 
(For further details, see Pages 15-16 of A.S. 1349 1986).

 

For acetylene, safety pattern gauges MUST be used.  (For further details, see page 16 of A.S. 1349 1986).

 

For steam and gases other than oxygen and acetylene, gauges of normal construction may be used for
pressure ranges up to 2500kPa but blow-out disc should be incorporated.  For higher pressures, safety
pattern gauge MUST be used.

 

Jointing

Where parallel threads are used on the shank, the joint MUST be made on the flat seating using a washer
of suitable material.  The joint on the seating washer MUST be tightened by means of the hexagon or square
provided in the screwed shank and not by grasping the case.

 

Maximum Working Pressure

While gauges will withstand a full scale pressure, it is recommended that the working pressure should not
exceed 75% of the full scale range for steady pressures and 65% of the full scale range for fluctuation pressures.

 

Pulsation

If pressures are expected to pulsate violently, oscillate with high frequency or occur with sudden shock,
the manufacturer should be consulted.

 

Mechanical Vibration

Gauges should be mounted away from vibration and connected by means of flexible piping.  If this is not possible,
the manufacturer should be consulted.  Where liquid filled gauges are used, a safety release MUST be
incorporated in the case.

 

Temperature

If used on steam or other hot gases or liquids, gauges MUST be protected by the use of an effective syphon
or other means.  A gauge is unduly hot if it cannot be grasped by the hand without discomfort.  It should be
remembered that gauges used on water may burst if exposed to frost.

 

Mounting

All gauges should be mounted in a vertical position unless otherwise agreed with the manufacturer.

 

Cocks and Valves

In order to allow the gauge to be removed for checking or any other purpose, a gauge-cock or valve should be
fitted.  These cocks or valves MUST be opened or closed slowly to avoid sudden changes of pressure on the gauges. 
Procedures should be established to ensure the cocks  or valves are secured in the open position during normal
operation.

 

Head Allowance

Where the gauge is used on liquid and is mounted substantially above or below the pressure point, a head
allowance may be necessary.
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