O-ring Or Wall Seal ?

[JPigg55]

Designing up a small surge milker for goats.
Anyway, I have to make a double slide valve.
Which would work better for this application o-ring or wall seal ?
Not sure if it matters, but will operate via a 14" - 17" vacuum.

 

[joshua43214]

This will work sort of like the sliding valves used in steam engines?
What is a wall seal? Some kind of packing?
Are we talking about sealing the valve face to the body or sealing the actuating rod as it passes into the valve body?

Can you link a pic of something similar?

Either way. Sealing a rod that moves is best done with packing, O-rings require lube, are prone to damage and cutting.
Sealing two faces that move past each other is best done with a well lapped surface and no seal, or something something synthetic like PTFE or Delrin (both od which are also prone to damage. A well lapped gate will hold a pretty high vacuum.

 

[JPigg55]

This will work sort of like the sliding valves used in steam engines?

Not really, more like a shafts in a bore with a couple ports. Need to seal ports off.

What is a wall seal?

Kind of like an o-ring, but flat surfaces instead of rounded.
Another possibility would be to use leather seals like the original surge milker.
I'll post a couple links later showing the original.

 

[4GSR]

To meet FDA requirements, either metal to metal seal or Teflon sealing material is required. Rubber reciprocating seal I don't believe is acceptable by FDA. There's lots of people out there making Teflon Based seals. Not sure if Urethane is FDA approved or not. If it is, be another sealing material to consider.

 

[JPigg55]

To meet FDA requirements, either metal to metal seal or Teflon sealing material is required.

Not really worried about FDA, not selling milk just for personal use. May sell some if it works, but not for commercial use.
Thanks for the Teflon suggestion, but think I'll go with leather. No of the parts will come in contact with the milk anyway. Any part that will I'm making out of stainless.

 

[Wreck™Wreck]

To meet FDA requirements, either metal to metal seal or Teflon sealing material is required. Rubber reciprocating seal I don't believe is acceptable by FDA. There's lots of people out there making Teflon Based seals. Not sure if Urethane is FDA approved or not. If it is, be another sealing material to consider.

You can buy Viton O-rings encapsulated in PTFE from McMaster, also square section PTFE cord in lengths, when backed up by a rubber O-ring as an energizer works well for fluid seals as PTFE has no memory. Many hydraulic cylinder piston seals use this method. Go to Hercules/Bulldog sealing products and look through their catalog for square section seals.
Like so https://www.herculesus.com/home.php?cat=1064

 

[Paul in OKC]

Have you thought a bout a poly pack type seal? We use them in a couple of tools we build at the shop.

 

[JPigg55]

Have you thought a bout a poly pack type seal?

No I hadn't. Wanted to use something cheap and readily available. Hoping to make them for sale, but didn't want to deal with replacement parts.
First considered O-rings, but probably not the best option for it. Thinking leather best way to go.
Thinking of making body from stainless with brass or bronze for the slide valve. Wasn't sure if differential expansion of the 2 different metals would cause binding with temperature swings due to potential outdoor and seasonal use to use tight tollerances without seals.
I'd post a drawing of my concept, but I'm a terrible artist, can make a stick man look bad.