Abrasive service 1

[richmc]

Currently i am trying assist an end user to specify a valve for use on:

Glycerine & fatty acids @ 180'C and requires to seal at full vacuum.
The valve currently installed has a glass filled seat which is being damaged after 3 months service and will therefore start to pass. Has anyone any ideas?

 

[JimCasey]

What is abrasive about Glycerine and fatty acids? Are the fatty acids crystalline, suspended in the glycerine?

What type of valve are you using now? Ball, Plug, Globe, Butterfly?

What size is the valve?

What is the system pressure when the valve is required to seal at full vacuum? Is it 1 bar on one side and vacuum on the other, or 100 bar, or (pick a number).

Are you trying to modulate with this valve, or is strictly on-off?

How frequently do you cycle the valve?

If you will describe what the valve is expected to withstand, we can probably help you.

 

[richmc]

jim,

The current valve installed is a gemco spherical disc valve. The media has suspended particulates which can only be described as carbon based. The valve is 8" full bore design.

The system i understand is feeding the media through the valve from a vessel with approx 1 bar pressure. The operation is a batch process with the valve operated approx 5/6 times a day. The valve operation is on / off only.

It is critical to the process for the valve to hold a seal during process operation without drawing in any further product.

I have been thinking along the lines of a plug valve for the service but being 8" and full bore the actuation would possibly impact on the installation.

 

[JimCasey]

I looked at the Gemco valve and they seem to be marketing it as a shutoff valve for dry conveying.

I like your idea of a plug valve. You can get a higher-grade sleeve than virgin TFE for abrasion resistance, but with a plug valve there is SOOO much sealing area,and it tends to wipe itself clean. A plug valve such as a Durco Sleeveline lets you adjust the plug to restore the shutoff because the plug is tapered. Since it is on a vacuum service, you might check off on the specs that you want the supplemental o-ring stem seals. On a plug valve the primary seal to atmosphere is the circumferential band between the top of the plug and the sleeve. There is a supplementary diaphragm seal that is energized by process pressure (not vacuum) so the supplemental o-rings above THAT would prevent air inleakage.

The actuation is a consideration: A BIG double-acting rack and pinion, or if you need spring failsafe a scotch yoke actuator would be required. You might also think about a "Dribble control" package, to partially close the valve near the end of the batch, and to let it snap closed from a trickle flow exactly at the end of the batch.