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Thread: exp valve
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26-08-2004, 07:38 PM #1
exp valve
Hello all
Can you use an externally equalised exp valve as an internally equalised one if you blank off the 1/4 port with cap ?
regards
Bernard
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26-08-2004, 07:48 PM #2
Re: exp valve
NO!
Chemi
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26-08-2004, 07:52 PM #3
Re: exp valve
What do you think would happen if it was fitted
bernard
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26-08-2004, 10:54 PM #4
Re: exp valve
You can, however use an externally equalized TEV to replace an internally equalized TEV. Simply connect the equalizing line to the evaporator outlet and it will operate fine.
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27-08-2004, 02:11 AM #5
Re: exp valve
The constant pressure or automatic expansion valve responds to outlet pressure. It meters liquid refrigerant to the evaporator, maintaining a constant evaporator pressure. Refrigerant flows at a rate that exactly matches compressor capacity, and the valve incorporates a diaphragm that separates atmospheric pressure and system pressure with a range spring with an adjustable pressure setting is located above the diaphragm.
Beneath the diaphragm is a stainless steel push rod and ball assembly backed by a closing spring with an o-ring located on the push rod creates a balanced port. This feature balances out the effect of increasing or decreasing inlet pressure, and aids in maintaining a constant outlet pressure. IMPORTANT..An equalizer passageway is incorporated into the valve body and this is what you don’t have on a TXV. So if you insist on using a TXV you need to drill an equilizing passageway. This can be done but you need to talk to the mfg for the right size drill
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27-08-2004, 07:26 AM #6
Re: exp valve
I'm with Chemi
NO
Just get the right valve I mean £20 !!!???
There are three main forces in an ext equ. TEV the spring and the equalising line pressure to shut it and the bulb pressure to open it. The main closing force is the equalising line pressure.
GET THE RIGHT VALVE"It's better to remain silent and be thought a fool than open ones mouth and remove all doubt"
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27-08-2004, 09:14 PM #7
Re: exp valve
Inspired by Dan's post, you'd be convenienced to remember that if the evaporator consists of multiple parallel circuits then it'd be fed by a distributor which can have its own pressure drop normally much greater than the evaporator's pressure drop, with this application type you MUST use an externally equalised valve.
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27-08-2004, 09:27 PM #8
Re: exp valve
Originally Posted by frankIt's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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27-08-2004, 09:28 PM #9
Re: exp valve
hello blue boy
Its not a question of money,it was curiosity and to confirm something I,ve seen on site.
regards bernard
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28-08-2004, 07:57 AM #10
Re: exp valve
Originally Posted by frank
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28-08-2004, 08:03 AM #11
Re: exp valve
Originally Posted by frank"It's better to remain silent and be thought a fool than open ones mouth and remove all doubt"
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28-08-2004, 08:05 AM #12
Re: exp valve
OH I see Bernard I did not mean to apear bolshy. It does not change my answer however
"It's better to remain silent and be thought a fool than open ones mouth and remove all doubt"
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28-08-2004, 01:07 PM #13
Re: exp valve
I remember posting a reply in one thread stating that I was taught that a "rule of thumb" way to remember about TEV's was that if the system had a distributor then you should fit an externally equalised TEV. I also remember that this remark was not widely accepted as true
When selecting a thermostatic expansion valve (TEV) for
use with a Sporlan type distributor, an externally equalized valve must be used to compensate for the distributor
pressure drop.
BULLETIN 20-10
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28-08-2004, 01:28 PM #14
Re: exp valve
I think I understand, Marc. Your observations regarding hunting, and possibly flooding are very interesting and plausible, whereas, I would normally expect only evaporator starving to occur with an improperly applied internally equalized valve. I believe your friend's scenario is what happens when we try to compensate for that starving with TEV adjustments.
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28-08-2004, 02:57 PM #15
Re: exp valve
Originally Posted by Marc O'Brien
If you have more than the equivalent of a 2°F pressure drop across the evaporator coil, your best bet is to use an externally equalized TEV. A multi-circuited evaporator with a conventional distributor will require an externally equalized
As the Prof recalls, Sporlan played around with internally equalized TEVs having thermostatic charges that were compensated for distributor pressure drop for Carrier in the 1960s. The problem with this approach is pressure drop across the distributor varies as the load varies, causing the TEV to flood at light loads and starve at high loads, making it not much more effective than a capillary tube.Prof Sporlan
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28-08-2004, 03:16 PM #16
Re: exp valve
Originally Posted by Marc O'Brien
Starving can be expected. Since distributor pressure drop is roughly proportional to the square of the refrigerant mass flow as noted above, disrtibutor pressure drop can fall well below expected values which can lead to distribution problems, hunting, and possibly some flooding.Prof Sporlan
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29-08-2004, 07:11 AM #17
Re: exp valve
Originally Posted by Marc O'BrienIt's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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