"Selfseal" Test Plugs
The test plug is usually
screwed into a BSP socket welded to a pipe. Some valves, pumps or other items
of plant are provided with suitable tapped bosses which
can be used. Screwed pipe tees can also be used.
It is suggested that the
socket is welded to a pipe and a hole then drilled in the pipe before fixing
the test plug. An 8mm hole will be suitable for all sizes of probes.
It is also suggested that
the plug be positioned in the lower half of the pipe where possible. If fitted
in the top, a pocket will be formed which can trap air and, when the pressure
probe is inserted, the air will enter the probe. This could affect the pressure
reading. Where this is unavoidable a spare probe can be used to bleed off the
air before taking the readings.
Further reasons for
suggesting this location are:-
- The formation of the air pocket can encourage corrosion
at the boundary between the air and the water.
- It is usually easier to reach the underside of a high
level pipe and insert the probe during testing.
- Where flexible pipes are used to connect to the
measuring instrument, they will hang down rather than kink or pull the
For low level pipes, the
above considerations may not apply and the performance of the test plug itself
will not be be affected by the angle of fixing. If
the socket is fitted on the underside of the pipe there may be a collection of
sediment or scale.
This will not affect the
operation of the plug but may cause blockage of the pressure probe. Ideally
therefore the preferred position must be for the plug to be located at the side
of the horizontal pipework where possible, and
somewhat towards the bottom on high level pipework.
Wherever possible a pair of test plugs should be fitted at the same height.
It will be appreciated that
any pressure measurement is affected by the standing water height in the system
and the static head above the point of measurement. If readings are being taken
between flow and return, to determine the pressure drop across an item of
plant, the difference in height of the measurement points will be included in
the readings and must be allowed for. Where they can be at the same height this
factor can be ignored and the calculation simplified.
Always fit test plugs so
that they are accessible to probes. Thermometer probes can be up to 229mm
Procedure, pressure/temperature readings
- Slowly remove the cap from the plug. If, while doing so
you feel or hear gas or liquids escaping, quickly retighten the cap.
Determine at this time if the plug has been used improperly, and if
necessary replace the plug as soon as possible.
- Having determined that the plug is operating correctly,
remove the cap.
- Select the appropriate probe for pressure and/or
temperature. Lubricate the probe. Examine the probe for any sharp burrs
which would cut the plug core. Remove any burrs before using. Do not use
non-standard or damaged probes.
- Determine approximate pressure in pipeline and select a
gauge of suitable range complete with test plug adaptor/probe.
- Partially insert the lubricated pressure adaptor/probe
into the test plug. If you are not sure of the pressure behind the plug,
be prepared to quickly withdraw the probe before rupturing or over-pressurising the gauge. The plug, in its static state
and without a cap, can easily withstand over 35 BAR, 500 PSI
without leaking. Do not assume that, since the plug is not leaking, that
it is safe to quickly and fully insert a low-range gauge. If you guess
wrong, then the pressure gauge could explode in your hand.
- When the pressure gauge needle stops moving up-scale,
then fully insert the probe and read the pressure.
- Do not leave the probe in the plug any longer than
necessary. Always screw the adaptor/probe union to the top of the test
plug to prevent the internal pressure from ejecting the instrument and
- When removing the probe, do not place your face near
the plug. The plug should not leak when you remove the probe, but always
observe safety precautions.
- As soon as the probe is removed, replace the cap.
- Temperature probe insertion is similar to pressure
probe insertion with the exception that the operator should always first
determine the pressure behind the plug before insertion of the temperature
probe. This establishes that the plug is operating within its
specification limits. After pressure has been determined follow steps as
outlined in the Pressure Probe Insertion paragraphs above.
Test Plug Which Has Been Installed And Unused For Several Years
- Follow all operating procedures shown above.
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Falklands Road, Boyton
Hall Estate, Haverhill, Suffolk, CB9 0EA, United Kingdom Tel: +44 (0)1440 704201/763167 Fax:
+44 (0)1440 763121.