Posted by Chris Severance on May 26, 19100 at 11:41:44: via: n3-port223.modempool.com or 198.109.217.223
In Reply to: Warren - Response Please on Venturi Pump posted by Jamie on May 26, 19100 at 05:12:19:
>has a difficult time retaining pressure
A 5HP compressor has no trouble keeping the vacuum/pressure. It keeps right up but is worked to the limit. It will shut off periodically showing that it is keeping well ahead.
All you need to know if your pump will be suitable is a vacuum boiling chart. Robinair has one in their catalog and there is one right here
http://www.delanet.com/~pparish/vac-tabl.htm
Careful though, there are errors on this chart and on Robinair's chart. Hopefully someone will use a spreadsheet and not an adding machine to derive these charts and eliminate the errors.
Using this chart I see that water will boil at 78*F at 28.94" of vacuum. The $10 Harbor Freight special only advertizes 27.5" of vacuum so that one will not be suitable. The best truth I can get from the Mastercool at JCW is 29.5". The Robinair is 29.7". Both would be suitable but the Mastercool requires 90psi@4.5CFM. The Robinair only requires 75psi@4.5CFM. With the Robinair the compressor will last much longer.
>why do you sell them
Someone needs to sell them or the DIY user will be priced out of the market. Go to NAPA and you will find that the rebadged Mastercool venturi vac costs $250. Hmmm, for $289 I can have a dual stage Robinair motor vac.
Stationary systems are where dual stage high vacuum pumps are necessary. You won't live long enough to finish evacuating a 20 ton chiller with a Robinair venturi vac. The bit of remaining air and water will destroy the system.
>it is biased by many for only what profits them and is in their best interest
If only we can get everyone to be equally greedy then utopia will have been reached.
Your opinions come from people with this kind of varried experience. Some know the value of a deep vacuum and some are content with the 24" that a car engine can produce. I will use my Robinair vac until there is a dual stage vac pump available for cheap.
>Your product line venturi is pricey,
Neither the venturi nor the motor vacs are pricy at ACSource. Only the Harbor Freight cheapo is any cheaper and that isn't worth the metal it's made of. I checked at my local Carquest and the same Robinair venturi vac is $80. Motor vacs at JCWhitney are single $299 and double $379 on sale.
I don't work for ACSource, I've just checked enough prices to know where the values are.