PVC water pipe for roughing pump

[John Taylor]

Has anyone used PVC or CPVC water pipe between their roughing and high vacuum pump? And if so, how well did it work? I have a 3" diff pump with a Welch 1402 and I'm wanting to change up their positioning. If this would work it would be very versatile (and cheap!). I currently use a piece of 1" copper flex, but it is only 24" long. I'm looking to reduce vibration on my baratron.

[Deleted]

All the vacuum plumbing I've done so far has been in copper or stainless, so I'm not sure how helpful my input will be, but PVC and similar materials tend to outgas heavily under vacuum, so it certainly wouldn't be as effective as copper or other metals. However, Kurt J. Lesker and other companies make a variety of PVC foreline tubing, so it seems quite usable on the rough vacuum side of things.
http://www.lesker.com/newweb/flanges/fl ... cfm?pgid=0

I've seen plenty of people on the forums using it with good success.

[Chris Bradley]

Has anyone used PVC or CPVC water pipe between their roughing and high vacuum pump? And if so, how well did it work?

There should be little problem with it because the backing pump is pumping a much higher pressure and so a few contaminants added in by the pipe are no big deal on that side of the high vacuum pump. However, what you may want to trouble yourself with is that these pipes are not really intended for quality, leak-free fitments so it is not so much the material you will struggle with but the capability to form good, leak-free connections with this sort of pipe.

[John Taylor]

The main reasons for wondering about water pipe PVC were ease of obtaining, low price and hopefully some elasticity to dampen vibrations. Without the addition of plasticizers used in the more flexible PVC "hoses" I thought outgassing would be less of a problem. The fitting issues will probably not be a problem, because I could (hopefully) attach metal fittings to the ends and seal with an epoxy such as"JB Weld". I've used this to seal quite a few connections in the past with good success at lower temps. I am going to go ahead and try this just to see what happens, but I may end up ordering a stainless bellows type hose in larger length and diameter.
By the way thanks for the advice!

[John Taylor]

I have begun construction of a PVC foreline to see if it will even work. I decided to use flexible PVC tubing at two joints to ease disassembly/reassembly plus give more isolation to reduce vibrations. I got couplings, elbows and a threaded connection to fit the mechanical pump end, but there was none to fit the diff pump end, so I threaded a PVC coupling to fit the diff pump end. I was originally going to attach metal fittings to the ends for pump connections, but decided against it in favor of the much easier threaded connections.

To make connections for the flexible tubing, I first made a groove around the end of each coupling on a table saw to help hold the hose in place and then heated the couplings over a burner until soft and rolled a taper in the end to ease insertion into the hose. I have enclosed photos to help explain all of this.

If any of you see any obvious mistakes, please let me know. I am going to let this sit under a warming lamp for a couple of days to dry out as many of the volatiles from the PVC cement as possible. In a few days, I will try it out and compare pump down times ( I will have more volume now and more length, but a larger inside diameter and it will be smoother than the copper flex).