Depending on how large is large, it will be far easier to replace the seat if worn instead of the complete valve (and for sure cheaper). On small valves, typical 2"-4", it would make little sense to replace the seat as it most likely will be cheaper to replace the complete butterfly valve (if it's a low cost trim, typical cast iron body and 316 stem /disc/buna n seat). We use eccentric butterfly valves for throttling (low pressure / high flow application) and would not recommend the use of vulcanized seats as the seat typically would be replaced each 3-4 years.
AWWA valves frequently have bonded seats. AWWA valves are designed by a committee to be mediocre and interchangeable.
Name-Brand valves including, but not limited to Bray and Tyco-Keystone have replaceble liners that lock into the body and provide the gasket surface as well as the seat.
Liners versus vucanized. You first have to ask your self how critical is the system the valve is in. If the system can not be down long you may want to look at a complete valve to change out. Up and running quickly. But this can also be pricey. Replaceable liners will allow for you to change out and repair on site. It will also allow you to stock several types of liners depending on what you are pumping. EPDM, PTFE, BUNA etc. You can engineer one style body with the different liners. Much more versitile. Don't count pennies at first engineering if possible. Saving a few dollars on cheap valves can cost major dollars down the road. Liners are not necessairly cheaper also. I am presently repairing an 8" Fisher B/F with a PTFE liner. As a distributor and repair facility, my cost for the liner is $1500.
I have come across this before and previously learnt that Vulcanized seats are mainly and mostly used for Vacuum Services... Keep in mind that if your service requires you to change the seats often then the vulcanized seats needs to be burnt off first... (I'm new here and hope I was helpful)
poppeye, our case is as follows: we are using large diameter replaceable EPDM liner valves (up to 1500 mm) for a buried chilled water network, the valves are located in valve chambers. We faced a situation where some contractor hammered on the branch pipe connected to the main (where the valve is), as a result the liner was damaged. I belive if it were a vulcanized liner it could have withstood the hit. However, we had to remove the valve completely and then change the liner. As you mentioned the liner was not cheap (specially at such sizes). I concluded that at such sizes and in critical installations (such as buried networks) it is better to use vulcanized liner even if you will have to change the whole valve and even if it will cost you more. We can always have one spare valve from each size or so.
HeshamM, Hammering on a branch line should have not damaged the liner. EDPM is very resilient and can stand a lot of punishment. I would look first at piping alignment. Did the contractor have to use chainfalls to get piping in line to put the valve in place? Gross misalignment can warp the body and cause the liner to flex. Over time the disc will tear away part of the liner and cause the valve to fail. This will happen with a vulcanized or replaceable insert type. With our new pump and valve sales, either myself as the Service Dept. Manager, our Sales Engineer or one of my Technicians is on site to inspect piping to ensure chainfall tricks are not being used by the piping contractor to meet deadline. We really have ticked off quite a few contractors but the end user is very happy in the long run that we did. It sure saves a lot of finger pointing later on.
poppeye, before the hammering, the pipes were aligned and inspected. They did use chainfalls to get the pipes aligned but this is normal practice for large pipes. The other contractor was excavating without considering the existance of this branch line. The welded branch connection was damaged severly. Some kind of a twist occured between the valve flange and the main pipe (connected to the branch) flange. They removed the valve by cutting the pipes, the liner was deformed to take an oval shape. It was a serious damage and maybe I shouldn't have used the word hammering but its quite a hit. Still I think if it were vulcanized it could have hung on there.
