Rolls-Royce Silver Cloud II - Page 27

Air Conditioning
System Manual
------- Rolls-Royce & Bentley -------------
bellows system. The interior of the bellows is con-
nected to the valve chamber by a single drilled hole.
The bellows exterior surface is subjected to
pressure governed by the phial clipped to the
return pipe from the evaporator and connected to
the valve by a capillary tube (see Fig. 2).
Expansion and contraction of the bellows operates
the valve by moving three pins , which act on
a
spring-loaded piston attached to the valve seat.
The spring tension is varied by means of an
adjusting spindle, the squared end of which is
protected by the capnut at the base of the valve.
Adjustment of the spring tension 6ffectively
adjusts the degree of superheat; this is set during
initial testing at the factory and should require no
re-adjustment.
In the event of adjustment being necessary , it
will
be noted that one complete turn clockwise of
the spindle corresponds to approximately 3.6°F.
(2°C.) decrease to the superheat. . The cap must
always be tightened after each adjustment, other-
wise refrigerant may escape or moisture may enter
the
system.
THE FLOW CONTROL VALVE
The flow control valve is mounted midwa)
along the right-hand valance and is connected in
the by-pa ss line between the compressor pipe and
the condenser.
The purpose of this valve is to maintain a.
minimum pressure of 2 lb ./s q. in . on the low pres-
sure
side of the system. To maintain this pressure,
high pressure va pour from the condenser is cooled
by expanding it through the valve, before re-
introducing it to the suction side of the
compressor. This prevents too heavy a pressure
drop in the compressor crankcase, which could
ca use priming of the oil.
Pa ge20
Fig . 15 Flow control valve
The outlet port ( compressor suction line) is
directly connected
with the valve chamber and the
interior of a spring-loaded bellows system. The
beffows exterior is subjected to pressure in a sealed
chamber; thus the valve chamber pressure acts in
opposition to the spring force and the pressure in
the sealed chamber.
When the s uction line pressure, and therefore
the
valve chamber pressure , falls to 2 lb ./ sq. in.,
the valve will be
opened by the spring.
A
combined friction and bellows damping
device is incorporated to prevent too-frequent
valve operation caused by rapidly fluctuating
conditions.
An adjusting screw is fitted in the top of the
valve
to vary the spring force and thus the valve
opening pressure. This is set during initial testing
and should require no further adjustment. Should
adjustment be necessary, the screwed cap must
always be tightened afterwards.