Re: Leaky safety valve
Posted by: Mark Drake
Date: September 26, 2012 08:21AM
I've gone through this with both of my condensers.
Both cars had a safety valve spindle turned to a conical 90 degree point - no ball. The 735 spindle is made from a decent grade of bronze, but started to leak after a couple of years use. I have since re-machined the cone and lapped it in with Brasso; it now does not leak after 4-5 years use.
The 740 had a spindle made of a rather inferior brass, and this started to leak substantially after 1 years use. On inspection under a microscope, there was a multitude of microscopic radial lines 'etched' into the seating surface of the cone. I suspect that very low level leaks actually eroded tiny paths in the surface of the brass, which got bigger with time; the sum of which was a large leak. I have since replaced the spindle with stainless 304 and lapped it in with Brasso - all's well so far.
These safety valves do tend to leak after they've been lifted for whatever reason (debris probably), so my view is that they should be overhauled if allowed to lift.
It's not a bad thing to take the valve off and test it on a hydraulic rig. I set both my SV's to 750psi and tested them with the inspector present, just to be sure. I then re-fitted to the cars while we drank tea and waited for the pilots to warm up!
I hope this helps - happy steaming all.