How to Make / Where to Buy Packing for Vacuum Cylinder?

[DB26]

Hello everyone,

 

I’ve received a lot of help from the members here on my other thread:
 

But now I need help regarding the packing on the other end the vacuum cylinders. I’ve tried to make my own with rope, but it never seems to work right. The seal is weak and the shaft does not move to full extension. Is there a way I can make a quality packing or buy some somewhere?
 

I haven’t impregnated the rope I’ve used with anything besides some light machine oil. Should I be using a grease or some sort of graphite? And I’m not sure what size rope to use. I’ve tried a thicker and thinner type and have had mixed results. Nothing that works just right. 

Edited March 19, 2020 by DB26 (see edit history)

[DB26]

Here are some photo of where the packing would go on the cylinder:

 

The gap between the shaft and the outer ring is about 5/32 big. 

 

[37_Roadmaster_C]

I have no experience with vacuum cylinders, but I would try graphite impregnated cotton "pump packing". It is available in many sizes and is square or round. I would use square and plan on cutting it for "Chevron" alignment. That may not be needed, but it may help a lot with vacuum sealing.  The packing material would be available at any motor/pump repair shop. Hope this helps.

[Bhigdog]

McMaster-Carr web site. Search shaft packing...........Bob

[Mark Shaw]

Sealing reciprocating shafts is much more difficult than rotating shafts.  These seals are usually directional to the high pressure side with V shaped sealing members that self actuate with higher pressure inside the V.  In vacuum applications, the high pressure side is just the atmosphere.  I believe you may need a cup seal:

 

https://www.mcmaster.com/piston-cup-seals

 

https://www.mcmaster.com/v-packing

 

 

[DB26]

Thank you everyone. I bought some rope packing from McMaster Carr. 1/8” just a tad smaller than my measurement. We will see if it works any better than what I have now. 

[DB26]

Well, I guess I measured wrong. Got my 1/8 graphite packing and it’s too thick. 
 

Does anyone know where I can get a smaller width packing? 
 

But in the mean time. I hammered down the 1/8 thick packing and sliced it in half with scissors. Seems to work, but haven’t tested it yet. We will see. 

[cahartley]

^  I've done that more than once over the years.......no problem.

In tight situations such as yours I also have unraveled thicker packing and wound in individual strings but we worked on a lot of irrigation pumps so had more to chose from.