Wednesday, 28 November 2012

Water Filter Valves

On the left hand side of Sentinel 7109's water tank, there is a pair of water filter valves. These valves are in line with the pair of pipes feeding the two engine-borne boiler feed pumps.
The pair of water filter valves (not a recent photo!)
There is a flange plate at the back of each valve which fits over a hole in the tank side. When the valve is opened, water is able to pass upwards through the filter and out through the pipe on the left hand side.
Filter valve section drawing
(from S-Type Waggon Parts Manual)
The above is the best drawing I've been able to find although this is a type made for mounting horizontally on a S-Type Sentinel Waggon. Just pretend the bung numbered '7' is at the bottom below the valve spindle!

An unusual feature of the valve is that it has two seats (10). The obvious one closes the water inlet to the right; less obvious is the seat to the left which closes when the valve is fully opened. This is to stop the water from seeping out through the valve threads. I guess this is a simple, low-maintenance alternative to gland-packing the valve spindle.

The filter element and other component parts are shown below.
Component parts showing the filter mesh
As I've described in a previous article, the assembled valve has a black cap to its right. This seals an outlet which formerly supplied an injector before the cab mounted boiler feed pump was installed.
Drain plug shown highlighted
There is a drain plug at the bottom of each valve which serves two purposes: firstly to drain the filter valve to prevent frost damage and secondly to allow rubbish to be emptied from the filter. Looking back at the drawing, the detritus collected by the filter will inevitably sink to the bottom of the valve housing. So, for a vertically mounted valve, this should work quite effectively.

However, Sentinel 6515, Isebrook, which usually lives at Quainton Road, has its filter valves inverted as in the photo below!
Isebrook's inverted valves
When I examined 7109's valves, one clearly had a frangible stud which has been drilled out and replaced with a nice shiny new one.
Stud frangibility...
... and the brand new replacement
Gasket material for these will be rubberised cork sheet as there is no high temperature to contend with and only low pressure from the height of the water in the tank.

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