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Q)
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How is a T.E.V. selected?
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A)
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The selection depends on the refrigeration duty, the evaporator
pressure and the pressure drop across the T.E.V. Should the
discharge (head) pressure fall this will reduce the pressure
drop and the flow rate through the valve. This will result
in a reduction in evaporator pressure and refrigeration duty.
This is why on some systems head pressure control is used
to maintain the pressure drop. This prevents the evaporator
pressure falling below 0 C and so causing the coil to freeze.
Refer to FAQ's -general topics
& FAQ's - pressure regulators
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Q)
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If the valve has an external equalising connection must
it be connected?
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A)
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Yes, or the valve will not regulate.
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Q)
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Why use a liquid receiver in a system fitted with a TEV?
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A)
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When set up correctly the TEV allows sufficient refrigerant
into the evaporator, such that it will all boil off and only
allow superheated gas to return to the compressor. Under high
load conditions there would be a smaller amount of refrigerant
in the evaporator so to store the excess requires a liquid
receiver. If the receiver was not used the liquid would backup
in the condenser making it inefficient during this period.
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Q)
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Why is a liquid receiver not fitted with a capillary tube
application?
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A)
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Normally a capillary tube is used where a relatively constant
load is being cooled, e.g in a domestic refrigerator, ice
cream freezer, bottle cooler and many display cases. To allow
for when a sudden high load occurs and liquid is carried over
into the suction line, a suction line accumulator is fitted
to catch any liquid before it enters the compressor. The refrigerant
charge of a capillary tube system is critical and so it must
be carefully weighed in during manufacture or servicing.
Note:
It is advisable to position the drier pointing downwards with
the capillary outlet at the bottom. This prevents the drier
acting as a liquid receiver and the possibility of overcharging
the system.
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Q)
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Are Parker T.E.V.'s factory set?
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A)
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Yes, Parker
valves are set with a static superheat of 8 F ( 4.4 C ). The
static superheat is the amount to just start opening the valve.
Should it be necessary to alter the superheat setting then
1 full turn clockwise will give an increase of approx. 3 F
(1.7 C). A normal operating superheat for most systems should
be approx. 15 F ( 8.3 C ) when measured close to the suction
connection on the compressor.
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Q)
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Do the Parker T.E.V.'s have interchangeable orifice sizes?
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A)
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There are two types of Parker expansion valves.
The C(E), S(E) and I series valves have a fixed orifice with
a ball seat and balanced port, which gives each valve a wide
operating range and makes them ideally suited for applications
where the required capacity of the valve varies e.g. in systems
where the head pressure is allowed to vary substantially.
The B(E)5 series are designed to accept interchangeable orifices.
By fitting the appropriate orifice for the required duty to
either an externally or internally equalised body, a B(E)5
valve can be ready for installation in minutes. Orifices are
sold individually or in boxed sets of 8. Designed as a drop-in
replacement for other similar interchangeable orifice valves,
a handy cross-match chart is available for the B(E)5.
Download B(E)5 cross match chart
(Adobe Acrobat file, 20KB)
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Q)
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How do I avoid flare joints as required by EN378 whilst
retaining the convenience of a flared connection?
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A)
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Flare to solder swivel connectors (our part numbers KRCY
in sizes from 1/4" to 5/8") are acceptable. One
end of the connector is soldered to the pipe, the other end
provides a machined female flare connection.
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