Three new ones are required on Sentinel 7109:
- A 1/2 inch type to isolate the vacuum braking supply.
- A 1/2 inch type to isolate the supply for a steam cleaning lance.
- A 1.25 inch type for the boiler's blow-down valve. (See later).
|The 1.25 inch and two 1/2 inch ball valves|
|Full bore when open|
The original blow-down valve was made from gunmetal with flange fixings. Whilst it looked the proper job, when I came to investigate the safety valve mounting flange requirements, I found that I would need a BS10 Table 'F' rated type made from Carbon steel. The Table 'F' flange is 1/2 inch thick which is somewhat more than the flanges of the blow-down valve. Add in that gunmetal is not as strong as Carbon steel and it becomes clear that the original would not be strong enough. Not having any specification to support its construction means that I really can not be sure it is good enough.
The ball valves pictured above are made from stainless steel with Carbon reinforced PTFE seals and are specified for 212 DegC and 275 psi. I thus have complete confidence that these valves will be strong enough. Also, to coin a phrase, they were 'Reassuringly Expensive!".