problem 16" knife gate valves

Hello, we have a pair of 16" knife gate valves that we cannot get to close all the way. We are thinking it is product buildup between the seals, but has anyone seen any other problems that are similiar? If so, what and how did you go about fixing it? I wanted to try an acid wash on the valve, but I'm not so sure that will work. Thank you.

 

A knife gate is generally used in poluted systems where particles like slurries are in the medium. In case these particles are tending to clog up, or you have fibres, you may have the problem you are in.

There are two problem areas 1. bonnet (in case there is one in your valves'design) 2. the bottom area.
what may help is a simple trick. While closing keep the valve in the lowest position for a while longer, velocity of the medium flush the area.

If this will not help you may consider a flush line. located close to the bottom seal area.
Better solution is after turnaround change the valve in a so called trough conduit valve. Here you have type of knife gate valve including a plate with hole. So there is no bottom area where the blade may stuck

Good Luck !
Ed

 

[petern1]

We use knife gates extensively in slurry services, and have had a number of issues getting them to close.

In some cases, the valves had origianlly been specified for pressure from one side only. This resulted in a valve ordered and installed with one way sealing, very little support for pressure on the gate form the non-pressure side. In actual fact during operation they received pressure from the non-pressure sode, and the gates bent, making them, difficult to close. You could check this by opening your valve fully and see if the gate has a bend in it.

In many cases we get rocks or sand build-up in the bottom of the valve. We have taken to installing the valve upside down, so that the seat stays clean. Not always possible to change in existing installations but should be thought about for new installs. We selected upside down over 90 degrees because the valves are actuated, and the actuator weight out the side would be too much bending on the yoke.

The idea from Ed to partially close and flush is good. This sometimes works.

Good luck