Brochure

Pressure Gauges
& Heating Specialties
F-6
Lynwood, CA [phone]
Curtis Bay, MD [phone]
PASCOSPECIALTY.COM
3/25/18
The following information has been gathered from various sources, including
AMETEK’s Pressure Gauge Handbook and ANSI B-40. The descriptions and topics mentioned
cover the particular gauges that are found in PASCO’s catalog.
Commercial Gauges:
Gauges found on much of the equipment used in manufacturing plants, stores, garages, etc. are classified as commer-
cial gauges or general purpose gauges. Typical equipment uses include refrigeration units, pumps, compressors and
fire extinguishers. In such applications, although the gauges may be ruggedly built, service conditions are not expected
to be severe. These gauges are of Grade B accuracy and could have metal or plastic cases and glass or plastic faces.
Commercial gauges are low in cost and designed without refinements to simplify maintenance or repair due to the fact
that it is less expensive to replace them than to repair them. Not for use on oxygen systems.
Grade B Gauges
GRADE B Gauges are used in the above mentioned general purpose applications. These gauges are often referred to
as 3-2-3 gauges. The reason is that they have a an accuracy of 2% of span over the middle half of the scale and 3% of
span over the first and last quarters of the scale. Grade B gauges are not high accuracy gauges, but suitable for
commercial installations.
Gauge Take Up
The average user believes that if the gauge pointer is not on zero, then the gauge must be faulty and will refuse to
accept the gauge or try to reset the pointer, damaging the gauge. As shown above, a GRADE B gauge pointer could
not be at zero and still be within spec because of the 3% accuracy at either end of the scale. A GRADE B gauge will
begin more accurate measurement once the pointer goes past the first 3 graduations of the scale.
Frequency Of Graduations
The frequency of the graduation on a gauge should bear a relationship to the grade of accuracy. For example, it is
somewhat misleading to divide the gauge into 100 increments if the gauge is made to GRADE B accuracy.
Pulsation Damper
Push checks or throttle plugs are the least expensive pulsation dampers. These checks are usually made from the
same material as the pressure port of the gauge and they are easily installed by pushing into the gauge stem. The
small hole in the check helps alleviate pressure surges or spikes which may cause gauge failure. In the event of gauge
failure, due to fatigue or corrosion, the check may also limit the flow of pressure medium if the gauge develops a leak.
The small diameter hole in the check may become clogged with debris preventing gauge operation. The gauge should
be checked from time to time and this hole kept free of debris.
Gauge Valves or Cocks - IMPORTANT
Gauge valves or cocks are installed in the pipeline leading to the gauge. The valve provides a means of shutoff so that
the gauge can be removed from the line without loss of pressure. The valve also allows the gauge to be completely
closed off from the pressure source except when it is necessary to take a reading. Clogging of the gauge stem is mini-
mized and the gauge will also be isolated from pressure surges or spikes. This arrangement will nearly prevent early or
unexpected gauge failure and greatly extend the life of the gauge.
Siphons
The purpose of the siphon is to provide a heat exchanger where steam in the line can be condensed and the result-
ing condensate cooled prior to entering the pressure gauge. This prevents the melting of the soft soldered joints of the
gauge which could cause gauge failure. A pigtail siphon is a coiled tube. This coil provides a large cooling surface and
the trap created prevents the condensate from draining away. Incoming vapor must pass through this liquid seal and is
cooled. This type of siphon is often referred to as a trap.
Installation
In all installations, ANSI B40. must be strictly followed. Always use the wrench flat on the gauge stem to tighten the
gauge into the fitting. Never APPLY TORQUE TO THE GAUGE CASE. It is suggestion that a joint compound instead
of thread sealing tape be used. Tape sheds can get into the pressure gauge port of the gauge causing blockage.