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Metering Valves - CO2
Ok, got back from talking to a few distributors and looking at all sorts of
specs for Nupro, Parker and Hoke metering valves. (All valves worth looking at
are metering valves - any valves specifically labelled "needle" I've seen specs
for, are terrible by comparison. They are all far too coarse.)
First, let me get the one I'll be skipping out of the way. Hoke has a very
sorry-looking web site and unfortunately doesn't feature much content. I'll
hopefully get some literature soon though (on the Micro). Prices on these sound
like they're much higher than anything else, but they do look like they
currently have the lowest Cv, bar none.
Last year Dan Dixon mentioned he had purchased a Parker HR1 metering valve
because he was unable to locate a Nupro S. This message is what turned me on to
Parker in the first place. His message to APD is available in the archives but
can be found without difficulty in the Needle Valve and Solenoid page at the
Krib. (Just search www.google.com for "parker dixon needle krib" if you can't
locate it by navigating the Krib's pages.
Dan posted the specs for the first five valves in the HR series. There are 7 in
total. The specs he posted, though very very nice, are unfortunately for the
older HR series. Parker has redesigned these valves and the information on
their web site is current as of this past July.
All HR feature max inlet pressure rating of 250psig, 15 turns to open and
complete shut-off capability:
HR0 - Orifice: 0.000002, Cv 0.0004
HR1 - Orifice: 0.000083, Cv 0.0070
HR2 - Orifice: 0.000168, Cv 0.0140
HR3 - Orifice: 0.000241, Cv 0.0200
HR4 - Orifice: 0.000674, Cv 0.0300
I only listed the first five for comparison to Dan's data. Also because the HR4
features the same Cv as the Nupro M (though it has a much smaller orifice). The
Nupro S falls between HR2 and HR1 in terms of Cv. The numerical designation
(HR#) in the series corresponds to the valve stem taper. I can only guess that
the number corresponds to the degrees (no other stat is mentioned).
The other very interesting aspect of these valves (likely because they don't
bottom out at a preset gap) is that their Cv vs. turns open is very smooth and
doesn't feature the small "bump" at the lower levels that the Nupro valves do.
Unfortunately there are no graphs for air flow rates (just water, which are
obviously lower than those of the Nupro valves).
I priced the HR1 valve today in a configuration that would more than likely be
at the bottom of its price range (the option of slotted vs. standard knob and
angle vs. straight pattern don't change the price). For a brass HR1 with 1/4
NPT ends and Buna-N seal, the price came out to $138 Canadian. That is roughly
$92 US (at a rate of 1.5 for safety). Oh, plus 15% tax. :)
I'm the kind of person that will sometimes go overboard, but that is just a bit
hard to swallow. Tonight I located another Parker series, the NS:
1 degree taper, 13 turns to open (+/- 1), Cv = 0.039 for straight (0.042 for
angle), rated to inlet pressure of 2000 psig, factory-set stem-stop at 2cc/min
flow at 80psig (!) - don't know if that's measured with water or air. If air,
that sounds super-slow, if water... Air will be significantly higher.
In addition this one is also available with a torque handle for very precise
adjustment. There are two more (NL and NM) valves with higher Cv.
Anyway, I'd really be interested in what people think of the specifics. I was
able to find Nupro S valves at only a slightly higher cost than M (+ $7-15)
locally. They were between $62 and $70 CAD (featuring 1/8 and 1/4 Swagelock
fittings). I will call for pricing on the Parker NS to see how much lower it is
than the HR series and to compare to the Nupro M.
As James also mentioned, hope people don't mind all the specs and tech info
being posted. There really isn't any better forum for this info that I know of
- unless someone were to start a tech-specific list. :)
I hope I didn't make a mess of anything. I've been driving and walking around
all day like a zombie (flu with full gamut of symptoms), in and out of
distributors for all sorts of stuff.