cate the actual discharge temperature; by pressing a but
ton on the front side of the read-out the set value of the
safety switch will be shoWn. The safety sw1tch is control
led by its temperature, sensing element fltted via a sealed
connector inside the discharge line close to the discharge
connection of the compressor. The discharge temperature
safety switch constitutes the most important protection of
the compressor, because deviations trom the norrnal oper
ating conditions (such as shortage of 011, toa high an oil
temperature, too high a pressure ratio, excessive super
heatfng of the suction gas) are always leadîng immedi
ately to a considerable rise of the discharge tempe,ature.
- An electronic Mmaximum oil temperature
n
safety switch
{30k) which guards the temperature of the oil leaving the
oil cooler and can be set to a value between 0 and 65
·c,
This safety switch also incorporates a digital read-out to
indlcate the actual oil temperature; by pressing a button
on the front side of the read-out the set valt.Je of the safety
switch will be shown.
The temperature sensing element is fitted via a sealed
connector inside the oil discharge rnanifold.
-
A
Mmax. discharge pressure� safety switch (30e) which
protects the package and plant against a discharge pr
e
ss
ure beyond the desigri conditions or operating llmits.
- A "min. suction pressure� safety switcn (30f) which pro
tects the. package and plant against suction pressure
below the design conditlons or operatlng limits.
- A "max. suction pressure" safety switch (30i) which pro
tects the compressor agalnst excessive internal groove
end pressure due to a high suction pressure in combina
tion with the built-in pressure ratio of the compressor. lt
also keeps the compressor capacity control in the "min.
capacity"-position durîng starting of the package in a sys
tem with high pressure on the suction side.
- A "min. discharge/oii differential pressure" safety switch
(30h) which protects the compressor against running with
insufficient lubricatlng oil supply to bearings, capacity con
trol. slide valve and shaft seal.
-
A
second •min. discharge/oil differentîal pressure" safety
switch (30g) whlch prevents the compressor drive motor
trom
being started until sufficient lubricating oil pressure
has been built up by the lubrication (16a in fig. 3.2 and
3.3) or full-flow (1 Gb in fig. 3.4 and 3.5) oil pump. So, this
safety switch is only of importance during starting of the
pacl<age.
- A spring-loaded pressure safety valve (8) on the oil .separ
ator, which protects the package under any circumstan
ces against excessive pressure built-up. The valve is
factory-adjusted at 21.5 bar(e) and sealed.
- A pressure drop sensing switch (20a) fitted on the main
flow oil filter, to prov1de for a visiblé and/or an audible
warning signa! when the filter is clogging (pressure dif
ference has reached i bar)
.
All safety devices, wlth the exception of the spring-loaded
pressure safety valve and the pressure
·
drop sensing switch,
are mounted inside a closed cabinet on the package front
side as per fig. 3.9, which also contains ali pressure
gauges. In case a control cabinet has been delivered With
the package as wel!, the temperature safety switches, all
temperature measuring devices and capacity indicator are
located inside this control cabinet.
The safety switches are to be incorporated in the control cur
rent circuit of the package in such a way that the compres
sor stops as soon as one of the switches is actuated due to
an unsafe condition (reter also to the next paragraph 3.6).
3.6 OPERATION OF'THE STANDARD CONTROL
CURRENT CIRCUIT.
General
As the trouble-free operation of the compressor depends in
particular on the injection of the correct quantl'ty of oil into
1he rotor grooves and an adequate lubricating oil pressure
for the bearings, slide valve and shaft seal, the operational
sequence of the safety switches in the control current wiring
diagram is such, that the compressor can start and remain
in operation only, when the oil system works properly.
Therefore sufficient lubricating oil pressure should have
been built-up before the compressor can be started.
To ensure easy starting of the electric drive motor during
compressor start-up, the capaclty control slide valve must
be in its "minimum''-position and the by-pass va!ve between
suction and discharge (if present) should be o.pen.
When the package is at standstill, the healing element in
the oil separator shoutd be operating; its task is to keep the
viscosity of the oil low enough and to prevent, as much as
possible, the refrigerant from dissolving in the oil.
The foregoing conditions are met by the control current wir
ïng diagram shown in fig. 3.9. This control current circuit
comprises the following safety switches:
- Therrnal protection of compressor drive motor (F1) and
automatic thermal protection of oil pump motor (F2);
,
•
.
Max. discharge pressure safety switch (S5), min. suction
pressure safety switch (86) and max. suction pressure
safety switch (S3);
- Min. differential pressure safety switch between oil and
discliarge pressure (S13) whîch prevents the compressor
drive motor frorn be1ng started until sufficient lubricating
oit pressure has been built-up by the ,lubrication or full
flow oil pump. So this safety switch Is only of importance
during starting;
-
Min. dîfferential pressure safety switch between oil and
discharge pressure {S4) to ensure sufficient lubricating
and injection oil pressure after the starting period;
-
Max.
oil and max. discharge temperature safety switch
(S7 and S8 respectively);
-
Pressure drop sensing switch (S9) on main flow oil
fil
ter
;
-
Max.
and rnin.
lrmit
switch (S 16 and S 17) of the capacity
control slide valve actuator.
Starting the package
When the compressor package is at standstill and the main
switch S1 Mis closed, the capacity control slidê valve actua
tor moves automatically to the position �minimum capacity".
Page3.12
Compressor Package GSLP
92.01
