Backflow prevention in vacuum service

Is there a type of valve/device that functions to prevent flow in a vacuum distribution from going down a line other than the main header. The attached sketch shows my situation better.

I believe I’m looking for a check valve, I’m just not sure an appropriate type exists for my situation. The vacuum line itself would be a 1" or 1.5" stainless steel tube (small chance it could be pipe instead). This type of situation is one where I’d outright segregate the vacuum users to different pumps, but I was in a conversation where backflow preventers were mentioned in the context of a vacuum system - unfortunately I couldn’t get the speaker to clarify their meaning during the conversation.

SKM_C300i22061316290.pdf (164.2 KB)

Hi @jari001

Backflow preventers I’m familiar with are to prevent contamination of a high pressure utility.
They have dual check valves in series with a relief to atmosphere in between. It is a high integrity, more complex back flow prevention system than a single check valve. I think these sprung from the drinking water, city water industries to avert contaminating/poisoning drinking water supplies.

I doubt you need that level of integrity in a chemical process, but it’s your call. I think a simple, single check valve will do what you want reliably, especially if it is a clean, non-corrosive service

@Latexman I also associate “backflow preventers” with plumbing services but not CPI applications. In this case I’m working on a pharma project where the idea is to evaluate a common header system between multiple suites but we want to prevent cross - contamination as each suite could be a different type of product. I’ve not seen check-valves used in vacuum lines, are there particular vendors or types you could make me aware of? I work with Busch often, so I have a line out to my contact there at the moment.

@jari001 For SS check valves I’ve seen Kitz, DSI/Forum Energy Technologies, Bonney, Velan, and Check-All check valves used in our plants. I’d say the majority are Kitz and Check-All. IIRC, all Check-All’s are spring loaded.

What you need is a check valve with a very low cracking pressure, made from materials that are compatible with your process. I have used “quick exhaust” valves designed for pneumatic cylinders where the flat rubber diaphragm has been replaced with a fiberglass reinforced Teflon disc (Flapper Pneumatic Quick-Exhaust Valve Assembly | Schlumberger). You may also consider “duck-bill” types or ball-type check-valves that are mounted so the weight of the ball is all that controls the cracking pressure. The ball can be plastic or hollow for reduced weigh. For vacuum service you would use a far oversized valve for the flow (like a 3" valve in a 1" line).

If you need high reliability or the consequences of failure are serious, you need to go with actuated control valves and pressure sensors. Low cracking pressure means low closing force, so dirt and contamination can case these valves not to seal well.

@compositepro @Latexman
I forgot to mention the vacuum range in the OP. I’m looking at working pressures ranging from 7.5 to 100 torr. (The range of pressures basically means two pumps in my mind unless I want to use PCVs to maintain 100 torr at many use points, which I’m not sure is warranted just yet - but I digress.)

My manager said he used a similar strategy, but had an ON/OFF valve with a dP transmitter that initiated an interlock if the header pressure became higher than the use point pressure.