BF VALVES

[hyari]

regarding sewage treatment which Butterfly is preferred , double eccentric or centric design ? lose liner or volucnized rubber ? and why?


regards
ahmad

 

[Danlap]

Hi Ahmad

I think you just paraphrase your previous inquiries.
So I will also paraphrase the comments.

First, understand the nature of double eccentric and centric design.
Centric design have bigger potential of leaking (this is debatable of course) and within times it is often found susceptible for Disc offset (more than 90 degrees movement).
As in double eccentric, the preliminary (tight) shut off is more assured, and Disc offset possibilities is less to none.
It is just to name a few among other advantages and disadvantages for both design.

Some end users who already define BF matrix selection, are leaning towards using Centric design only for water application (non-brackish) and other clean service, and whenever Leakage is allowed (at some rate).
And after some time, whenever the leakage is beyond desired (also add into consideration whether another block valve on downstream side is available or not). The centric BF should be easily replaced.
Therefore, if the BF is underground (requires civil work or other hustle to remove it), Centric BF might not be appropriate. You need longer lifetime BF Valve (double eccentric or triple eccentric).

What some sort of lining? Lose liner or vulcanized rubber?
In general terms lose liner often perceived as PTFE, and sometimes EPDM. And vulcanized rubber are either EPDM or NBR (and requires heating process afterwards)
1. Understand your service (chemical content of the sewage), how it will react against those lining material. Contact your process engineer and vendors
2. Shall the expected lifetime of Lining is short (2-5 years), valve is relatively small, and your Plant's workshop (not involving vendors) can replace the Lining by themselves (assuming they don't have the rubber heating equipment), then maybe you could choose the lose liner.
PS: bare in mind that if the lose liner not well fitted, it may obstruct with Disc whenever operated. Thus, premature fail will occurs - liner broken (often see this happened to PTFE for BF after being re-work)

Regards,
MR

Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[gerhardl]

Use the bar at the top of this page and search for 'sewage' in this forum only, and you will get alot of comments on valves for sewage.

I would not use butterfly valves for sewage. As explained above BF valves will only be suitable if there is no fear of clogging or sticking. Depending on quality of bothe, double eccentric will have closing and opening geometru better than centric, and in most cases also better flow caracteristic.

Hole vulcanised discs have a high price, but are generally good. Screwed on disc aealings for double eccentric valves, change- and adjustable are a good solution. Centric BFL valves are not always suitable or allowed as end-of-line valves.

Chemical and leakage problems: Ref. Muktiade above.