Spirax Control Valve issue

[pal]

We have had similar issues with a spirax steam valve - the valve wasn,t completely closing and the slight leak-past caused erosion. Two things to check . First the air supply must be high quality dry air. There is a very small filter behind the air inlet fitting on these valves . ( We have very good qality air in our plant but unfortunately the valve got plumbed into a lubricated air point after the emergency stop valve feeding cylinders . This was not discovered for some time . OOOpps ! )
The second issue was that the valve was supplied with the controller seperately . The feedback positioner used a magnetic connection and was not quite near enough to the controller and vibration occasionally caused problems . The controller does have an lcd display of the valve position , so check that the valve is responding correctly . ( Again it took some time and a lot of head scratching to find this out. It was solved by getting the magnet closer to the controller .)
Our valve has now been trouble-free for over a year .
Paul

 

[Luke_Mages]

What is the damage being done to the valve? erosion of valve seat?

Not yet, the seal around the shaft that turns the ball is being destroyed, allowing steam to pressurize that shaft bearing surface and causing it to seize. At least that's the theory that makes the most sense right now.....

 

[The Plc Kid]

Your mechanics give it 10 minutes? You're lucky, mine will dig the hole deeper for a good half hour before turning over the original problem, and 3 more created during "troubleshooting", to me.

Dave

Sadly I must admit I have experienced that situation more times than I would like with my guy's also.

 

[Andybr]

A couple of years ago I had a really strange problem when using a Spirax SP200 positioner with a Rockwell FlexIO analogue output module. With the output set at 0 and the positioner disconnected the module would output 4ma as expected. With the positioner connected the output would increase to about 5ma and the valve would crack open even though the value in the PLC was still 0. I never really got to the bottom of this and had to install a signal isolator between the Flex module and the positioner to resolve the problem.