The accessories of the compressor include those
devices and systems with which the efficient
operation of the compressor in the installation can
be promoted and checked and those which, in the
event of failures prevent the compressor from
being damaged.
The accessories should be distinguished as follows:
A) Accessories the use of which has been
prescribed by the compressor
manufacturer,among which:
•
Pressure gauges for suction pressure, discharge
pressure and oil pressure; in the case of two stage
compressors also for the intermediate pressure;
•
Pressure safety switches for discharge pressure
and lubricating oil pressure;
•
For two-stage compressors: Electrically operated ca-
pacity control (also to be used as run-in control with
which the compressor can proceed as favourably as
possible to two-stage compression during the time
the installation attains the operating conditions).
B) Accessories the use of which is deemed
necessary by the installation engineer,
amongwhich:
•
Suction pressure safety switch;
•
Cylinder head temperature safety device;
•
Crankcase heating;
•
For single-stage compressors: Manually or
electically operated capacity control.
The choice of the accessories depends on the type
of plant, the refrigerant used and the operating
conditions; therefore, this choice will be
determined by the installation engineer.
In this chapter only those accessories are described
that can be supplied by the manufacturer of the
compressor. If other accessories have been
provided by the installation engineer, their
description can be found in the plant manual.
5.1 PRESSURE GAUGES
The pressure gauges necessary for checking the
correct operation of compresssor and installation
are mounted on a panel, each of them being
connected to the compressor via a shut-off valve.
For single-stage compressors three pressure
gauges have been provided, viz. a suction pressure
gauge, a discharge pressure gauge and an oil
pressure gauge; moreover, for two-stage
compressors, there still is an intermediate pressure
gauge.
The gauges indicate the pressure in bars; at a pressure
lower than the atmospheric, the pressure gauge
indicates a negative value. The scale of suction,
discharge and intermediate pressure gauges is
adjusted to the refrigerant in the plant, as besides the
pressure scale also the saturation temperatures
corresponding to te overpressures are given.
5.2 PRESSURE SAFETY SWITCHES
In order to protect compressor and plant, safety
switches for discharge pressure, suction pressure
and lubricating oil pressure are provided. They are
mounted on a panel and connected to the
pressure connections of the compressor via the
pressure gauge valves. The switch contacts are
incorporated in the control current circuit for the
drive motor of the compressor.
The discharge pressure safety switch
(Danfoss
pressure control type RT 5 for halocarbon
refrigerants, type RT 5A for NH
3
) protects the
compressor against excessive discharge pressure.
In case the preset pressure is exceeded, the
control current circuit is interrupted and the
compressor stops.
The suction pressure safety switch
(Danfoss
pressure control type RT 1 for R12, R22, etc. type
RT 1A for NH
3
) protects compressor and plant
against too low suction pressure. In case the
pressure drops below the preset value, the
compressor is switched off.
The switching pressure of both switches can be
adjusted by turning the main spindle after
removing a cap on the top side of the housing.
The adjustment can be read on a scale behind the
window in the front cover. Between the cut-out
pressure and the pressure at which the switch
makes circuit again, there is a fixed difference of
approx. 0.4 bar in the suction pressure safety
switch and of approx. 1 bar in the discharge
pressure safety switch.
Both pressure safety switches are provided with a
locking device when cut out, so that, on return of
the original pressures, the compressor does not
become operative automatically again. The
switches can be unlocked by pushing a green
button on the side; however, this may be done
only after the cause of the switching off of the
compressor has been investigated and the failure
has been remedied. In both switches an auxiliary
contact is provided for connection a pilot lamp or
a klaxon.
Refrigeration Division
Grasso
5. DISCRIPTION AND OPERATION OF ACCESSORIES
v002.97.10.en
Refrigeration Compressors Series RC9
Page 5.1
