Friday, 15 July 2011

Trailing Engine's Boiler Feed Pump

Whilst I had first run Sentinel 7109's engines on compressed air on 26th July 2009 and on subsequent occasions, I had not checked whether the Boiler Feed Pump (BFP) attached to each engine was in working order. Having renovated the Worthington-Simpson BFP, I was now much better prepared as to what I would find.

Engine BFP in-situ
Both leading and trailing engine BFPs look the same.

Part cut-away drawing
The cut-away shows that the pump is a reciprocating type driven from the crankshaft (or geared from the crankshaft).

Inlet (RH) and outlet (Left centre)valves
Access to the pump piston was not attempted as it would involve breaking and damaging one or more gaskets. From the Worthington-Simpson BFP piston design, I expect a similar multi-ringed piston forced on to the cylinder wall by the pressure of the water being pumped. I may be proved wrong! I was more interested in the condition of the inlet and outlet valves and how they were constructed.

Inlet valve to the right
Outlet valve below the 'bulb'

Inlet Valve

Cap on inlet valve chamber
Cap removed to show inner valve cap
Inner valve cap removed to show the valve itself on its seat
Valve removed to show its seat
Valve itself showing a clean surface
Valve seat in reasonable condition but would benefit from regrinding

Outlet Valve

'Bulb' instead of cap on valve body
The bulb is initially filled with air and provides a cushion to the pulsations of the reciprocating pump. It is similar in effect to a smoothing capacitor in an electronic circuit power supply.

Base of 'bulb' (just about) showing valve internals
Valve on seat with washer on top
I'm not sure of the purpose of the washer; however, it must prevent the valve from fully lifting and thus restricting the maximum flow. To me, it seems as if this might put an extra load on the engine for no apparent good reason - unless somebody knows better? It might also prevent the valve from coming out of its location but Sentinel were better valve designers than that weren't they?

Valve on seat with washer removed
Valve removed with washer in place on top
Valve seat slightly corroded (green)
and needing improvement by regrinding

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