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12950 W.Eight Mile Road ? Oak Park,MI 48237-3288 ? 248/399-8000 ? FAX:248/399-7246 ? www.trerice.com
1/1/2001
1
Process
Gauges
1/1/2001
1
1
1
What is a Pressure Gauge?
Selecting a Pressure Gauge
Case
Cases are available in a wide variety of materials and configurations. The
combination of material and configuration is generally determined by the demands
of the application, as well as the preferences of the gauge specifier. The more
demanding the environment, the more rugged
the case construction (i.e., polypropylene or
stainless steel for industrial applications vs.
aluminum or steel for construction or commercial
applications). Gauge mounting or retrofitting
needs may affect case selection (i.e., a gauge
to be panel mounted will require either a
front flange or u-clamp style case). For safety
considerations, a “solid-front” case style may be
required. Each application will have a unique set of requirements which will help
guide the specifier in selecting the appropriate case style.
Wetted Parts and Pressure Medium
Under normal operating conditions, only the tube and socket assembly (Wetted
Parts) of a pressure gauge will come into contact with the fluid being measured
(Pressure Medium). The selection of the assembly will be determined by the
composition of the medium. Air, gas, steam, water and other noncorrosive
media are usually satisfied by a bronze or brass bourdon tube and brass socket
assembly. Stainless steel or Monel wetted parts are used when the medium
contains corrosive elements or when high operating pressures or temperatures
will be encountered. A diaphragm seal is recommended for highly corrosive media
or that which may solidify or deposit solids within the tube and socket assembly
of the gauge. (See the Diaphragm Seal section of this catalog.)
DIAL
POINTER
RING
WINDOW
SEAL
SOCKET
CASE
BLOW-OUT
BACK
DIAPHRAGM
BOURDON
TUBE
MOVEMENT
SOLID
CASE
FRONT
Definition
A pressure gauge is a mechanical instrument
designed to measure the internal pressure and/or
vacuum of a vessel or system. Trerice Pressure
Gauges are offered in a variety of styles, sizes,
and wetted part materials to meet the demands
of standard and special applications.
Principles of Operation
Most Trerice Pressure Gauges are constructed
with a bourdon tube sensing element. When
the sensing element is subjected to pressure,
it flexes and the resulting motion is transmitted
as a measurement through a mechanical
movement to the dialface pointer.
All Trerice Pressure Gauges should be carefully selected to meet the
demands of the particular application. The information contained in this
catalog is only offered as a guide to assist in making the proper selection.
____________________________________________________________________
Improper application may cause failure of the gauge, resulting in
possible personal injury or property damage. For correct use and
application of all pressure gauges, please refer to Pressure Gauge
Standard ASME B40.100. This document may be obtained from the
American Society of Mechanical Engineers (ASME), Three Park Avenue,
New York, NY 10016-5990.
continuednextpage

Process
Gauges
12950 W.Eight Mile Road ? Oak Park,MI 48237-3288 ? 248/399-8000 ? FAX:248/399-7246 ? www.trerice.com
1/1/2001
2
What is a Pressure Gauge?
continued
Connection and Mounting
The socket connection provides an entrance port for the process medium as well
as a means to mount the gauge to a pipeline or vessel. Male connections can
be provided with NPT, BSPT, or other thread styles, in sizes from 1/8" through 1/2".
A high-pressure, 9/16" LHT Autoclave connection is also available. The mounting
location indicates where the connection protrudes from the case. Trerice Pressure
Gauges are available with three standard mounting locations: lower male (LM),
lower back male (LBM), and center back male (CBM). Other connection locations
may be available on some models.
Window and Ring
The window provides a means for viewing the measurement, as well as protection
of the dialface and pointer of the instrument, and is normally held in place by a
ring, which is screwed or snapped to the case of the gauge. Plastic, clear glass
and laminated glass are common window materials. Ring styles include threaded,
bayonet, friction, crimped and hinged, depending upon the case type.
Pointer
There are essentially three types of pointers available on Trerice Pressure Gauges:
a micro-adjustable pointer (providing high quality and accuracy); a friction-type
pointer (providing adjustability and durability); and a plain, non-adjustable pointer
(providing economic reliability).
Accuracy
The accuracy of a pressure gauge is expressed as a percentage (plus or minus) of
the maximum scale range. Please refer to Pressure Gauge Standard ASME
B40.100.
Measurement Range and Dial
The maximum operating pressure of the application should not exceed 75% of the
measurement range selected. Therefore, the specified range should be twice the
normal operating point of the gauge to avoid damage to the gauge internals. A wide
variety of measurement ranges is available, from 30" Hg vacuum through 20,000
psi pressure. Ranges are indelibly presented in black figures and markings upon a
white dialface.
Environmental Conditions
Pressure gauge selection will be influenced by the environmental conditions under
which the gauge is expected to perform. Condensation or waterproofing concerns
can be addressed through the use of hermetically sealed or weatherproofed
gauges. Case construction should be considered when selecting a gauge to be
used in conditions of extreme or sustained heat or cold, or where the atmospheric
environment may contain corrosive elements.
Liquid Filling
Liquid filling (glycerin, silicone or other fills) can prolong the life of a pressure
gauge by minimizing wear on the gauge internals resulting from vibration or
oscillation. Liquid filling also acts as a permanent lubricant to the moving parts
of the instrument.

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