In article <3qtofi$626@fohnix.metronet.com>,
~~>What is the reason for this??
Well, no one else is jumping in, so here goes....
A TXV ( Thermal Expansion Valve )is an interactive device, in that
it senses system ( evaporator ) pressure and temperature, and adjusts the
flow of freon so as to maintain a given superheat. Without this, the
coil would be starved ( not getting enough freon to work at capacity ) at
some times, and flooded ( too much freon, possibly damaging the compressor )
at others. There are several related devices ( for different purposes )
such as AXV, CPR, etc. that work in a simlar fashion ( to some extent ).
The TXV needs to see 'a solid liquid head' at all times, in other
words the input pipe to it needs to be completely full of liquid, in order
for it to be able to meter out the freon. There is typically a receiver
( holding tank ) to store excess freon, or else it is allowed to back up
into the condensor in some systems. This is extra freon in the system over
and above needed quantity to assure that at all times and operating
conditions, there is enough freon to 'present a liquid head' to the TXV.
Thus, seeing as the liquid line is designed to be at all times ( running
times, anyway )totally full of liquid, a visual reference is relevent.
Low level ( and some other problems) will show as bubbles or 'flash' in
the glass, giving an indication that there is a problem that needs
looking at.
Fixed ( non-moving ) metering devices, such as capillary tubes,
orifices, etc., on the other hand, never adjust to system conditions,
therfor standard fluid dynamics come into play, where a higher pressure
pushing in ( head pressure ), in relation to a lower resisting
pressure on the other side ( back or evaporator pressure ) means more
freon flow. Lower head pressures mean less flow. Thus, there is no active
control of superheat. If you were to charge a system of this type 'to
a full glass' under most conditions, you would be incorrectly charged
( generally overcharged, but actually undercharged in some cold weather
conditions ). Thus, having a sight glass would be misleading, as it
would be telling you a fact that is not relevent to correct charge.
This a rather 'quick and dirty' explanation, and I encourage
others to expand or correct as needed. :~)
Paul
In <3thl7f$oqo_001@grail409.nando.net>, pjm@nando.net (paul milligan) writes:
>Jim
Glad to hear it works now, but the color code is to designate the
refrigerant cross-charge in the power head ( green for 22, purple for 502,
etc., usually ). The size is in the number designation, such as 1 1/4.
The letters after the number designate other features, which I forget offhand,
but things like GFC, Z ( slow bleed port, I think ), and others.
Andy... You design the things.... got a list of the codes for us ?
TEV manufacturers have used the ASHRAE color codes to designate refrigerants.
Here are some......
Refrigerant Color
R-22 green
TEV manufacturers diverge with ASHRAE only on two refrigerants: R-12 and R-717
(ammonia):
Refrigerant ASHRAE TEV Man.
Why this discrepancy? These colors were assign way before my time, and I suspect
(actually I know) TEV manufacturers were a hard-headed bunch of folks back
then, and they probably disagreed with DuPont, and whoever was supplying
ammonia to the refrigeration industry. ASHRAE didn't exist at the time. ASRE
was the refrigeration organization, and they apparently didn't have enough
clout to knock heads together.....
Andy Schoen
> Glad to hear it works now, but the color code is to designate the
refrigerant cross-charge in the power head ( green for 22, purple for 502,
etc., usually ). The size is in the number designation, such as 1 1/4.
The letters after the number designate other features, which I forget offhand,
but things like GFC, Z ( slow bleed port, I think ), and others.
Alco, Parker:
The thermostatic charge is the constituents used in the sensing bulb. A 'cross charge'
indicates the 'bulb charge' P-T curve crosses the P-T curve of the refrigerant used in
the system. As a result, a 'cross charge' doesn't use the same refrigerant used in the
system the valve is being applied.
Nominal capacity is the rating of the valve in tons at 'standard conditions'. For R-22
and R-502, this is 40F evaporator, 100 psi across the valve, and 100F liquid refrigerant
entering the TEV.
Bleed ports can be added to any TEV. With Sporlan TEVs. it is indicated as a
'BP/
TEV manufacturers (for the most part) agree on refrigerant letter codes:
Refrigerant Code
We do disagree on a few, though. Here are some.....
Anyway, this is probably more info on TEV nomenclature than you really wanted to
know. :-)
Andy Schoen
Paul, FYI, Sporlan has traditionally abbreviated 'thermostatic expansion
valve' as 'TEV'. Alco has used both 'TEV' and 'TXV' in their literature, but
they typically use 'TXV'. They also use their 'thermal expansion valve'
tradename to describe TEVs, instead of calling the valve by their generic
name, i.e., 'thermostatic expansion valve'. Parker uses 'thermostatic
expansion valve', but abbreviates it 'TXV' like Alco. Guess that makes
Sporlan the oddball regarding the abbreviation. I believe Parker is simply
followed the lead of the previous owners of Parker's TEV product line, i.e.,
Jakes Evans and Detroit Lubricator. Ever see a Detroit TEV? Their #673
dominated the market in the 1940s. ASHRAE literature also uses the
generic name for obvious reasons, but it doesn't use an abbreviation,
probably in deference to Sporlan.
Actually, 'thermostatic expansion valve' is a misnomer, since the name
implies the valve controls at a 'static' temperature. Of course, the TEV
controls superheat, but 'superheatstatic expansion valve' didn't find
favor anywhere (for good reason :-)). Alco's 'thermal expansion valve'
is probably a better term, though it still doesn't describe what the
valve does. A hand expansion valve could fall in that category. Some
who have sought to rectify this 'problem' (university professor types,
primarily), and have used 'superheat control expansion valve' ('SCEV'
valve? 'SCXV'? :-( ) to describe it. But these same folks also want us
to publish all TEV ratings in SI units, i.e., degrees C, bar, kW (which I
could, but no one will read them).
Anyway, this is probably more than what you wanted to know about why
I call TEVs 'TEVs'.
Andy Schoen
jhuber@fohnix.metronet.com (Joseph Huber) wrote:
~~>In article
From: aschoen@mo.net
> I pulled the valve and compared it to another on the shelf to find the difference.
The body was the same, sized was denoted by color code and of course I had the
wrong color. Installed new valve and haven't heard a peep since 1984.
From Andy Schoen
R-134a sky blue
R-401A coral/pink
R-402A beige
R-404A orange
R-502 purple
R-507 teal (greenish blue)
R-12 white yellow
R-717 silver white
aschoen@mo.net
From: aschoen@mo.net
In <3thl7f$oqo_001@grail409.nando.net>, pjm@nando.net (paul milligan) writes:
Paul, TEV nomenclature used is as follows:
body type equalizer nominal capacity refrigerant code thermostatic charge
( omit if
internal )
Example:
HF E 1-1/2 H CA
Sporlan:
body type refrigerant code equalizer nominal capacity thermostatic charge
( omit if
internal )
Example:
G V E 1-1/2 Z
R-12 F
R-401A X
R-402A L
R-404A S
R-502 R
R-507 P
R-717 A
Refrigerant Sporlan Alco
R-22 V H
R-134a J M
R-500 D C
aschoen@mo.net
From Andy Schoen
aschoen@mo.net
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