Ashcroft a4a Manual de instalación y mantenimiento - Página 5
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BEZEL
EXTERNAL "ZERO"
ADJUSTMENT
Compound Gauge
Measures and indicates pressure
above and below ambient pres-
sure, using ambient pressure as a
reference point. A compound
gauge is a combination of a
gauge pressure and a vacuum
pressure gauge.
Absolute Pressure Gauge
Measures and indicates pressure
above zero absolute pressure,
using absolute zero pressure as a
reference point. All measure-
ments made with an absolute
pressure gauge will be positive as
it is impossible to generate a
pressure below that of zero
absolute pressure.
NOTES:
1. Ambient pressure equals pressure surrounding the mea-
suring element, generally atmospheric pressure.
2. The Ashcroft A4A absolute pressure gauge does not
incorporate automatic barometric pressure compensation.
The barometric pressure at the time of use must be set by
using the External Dial Adjuster.
Optional Features
Where specified, gauges have been equipped with auto-
matic thermal compensator, slotted link for protection
against sudden pressure release, peak load indicating
pointers or other optional features. See Section 2.3.5 for
Complete Details on Available Options.
2.3
CONSTRUCTION
2.3.1
CASE AND BEZEL
Solid Front Case
A solid front case of cast aluminum protects the operator
POINTER
WINDOW
WINDOW
GASKET
DIAL
CASE
when working with high pressure systems. In the event of
tube rupture through excessive over pressure, protection is
provided by this wall as pressure release will be directed out
the back of the gauge, away from the operator
Blow-Out Safety Back
A light gauge stainless steel disc, covering the entire back
of the gauge case, is spring-loaded against a seal
machined in the periphery of the case. An abnormal rise of
pressure within the gauge case causes this disc to flex out-
ward, releasing the pressure.
Bezel
A hinged bezel protecting the dial and pointer is equipped
with an external dial zero adjustment. It is also the mounting
for the lens.
External dial Zero Adjustment
A zero adjustment knob on the front of the gauge case
makes it possible to set dial zero to atmospheric pressure
or other benchmarks required.
Limit Stops
High and low pressure limit stops are mounted on the interi-
or of the gauge case, restraining tube tip travel within the
rated operating range of the gauge. The limit stops protect
the movement from becoming disengaged due to excessive
tip travel. They do not protect the Bourdon tube from dam-
age to over-pressure.
2.3.2
BOURDON TUBE SYSTEM
The Ashcroft A4A Bourdon tube is a product of more than
40 years of intensive, continuous research. The "unitized"
one-piece tube system is an outstanding example of mod-
ern technology.
Through exclusive Ashcroft A4A Bourdon tube designs and
manufacturing techniques, uniform stress distribution is pro-
vided in a wide range of tubes of varying cross sectional
configurations. All A4A tubes are formed from a single piece
of seamless tube material.
Tubes of 403 stainless steel are standard for ranges of 50
psi and above. Beryllium Copper may be supplied for low
5
PRESSURE
RELIEF
DISC
MOVEMENT
BOURDON
TUBE
PRESSURE
ELEMENT