Johnston VT501 - Water Pump

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MA4:3
V Range 501 l 651 l 801 Maintenance Manual
Johnston Sweepers Limited
Chapter - Water System
Page Issue A
The assembly of the twin diaphragm pump is quite simple and straightforward, but attention to the under
mentioned points will afford economy by prolonging the life of the pump and, more especially, the expendable
components.
1 Diaphragms -
When replacing a diaphragm, turn the crankshaft until the relative connecting rod is at TDC so that
when securing the diaphragm and the tension pad by means of the tension pad bolt, the periphery of
the diaphragm is free of the crank case.
Ensure that the tension pad is pulled down onto the connecting rod.
2 Pump Chambers -
Before fitting a pump chamber, turn the crankshaft until the relative diaphragm is at the centre of its
stroke, i.e. so that the periphery of the diaphragm is just resting on the face of the crankcase. Place
the pump chamber in position, place the bolts and nuts in position and tighten ‘finger tight’. Tighten
down, but make sure that the pump chamber is pulled down square so that the lower face of the
chamber is correctly located against the crankcase.
3 Manifolds and Valves -
Fit the valve sealing rings onto the valve seat. Place the delivery valve (stem upwards) over the
delivery orifice of the pump chamber and push the sealing ring down so that it is flush with the pump
chamber. Fit the suction valves in a similar manner, but with stem downwards. Place the manifold
over the valves and see that it sits square. If the manifold does not sit square, then either the valves
or the sealing rings are not correctly located. Place the securing bolts in position and pull down
squarely.
It is important that these instructions are carried out, especially with regard to the fitting of the manifolds,
to ensure a satisfactory seal at the valve sealing rings. Unless these instructions are followed, leakage
will be experienced at the joint between the manifold and the pump chambers. On dismantling a pump for
examination, if the valve sealing rings have taken on a permanent set to their location (roughly triangular in
cross section), they should be replaced.
M02MA-029
A
E
D
F
G
H
J
K
B
C
L
KEY
A) Manifold
B) Suction Port
C) Delivery Port
D) Suction Valve
E) Delivery Valve
F) Valve Sealing Rings
G) Pump Chamber
H) Tension Pad Bolts
J) Tension Pads
K) Diaphragms
L) Connecting Rods
Water Pump
COMPONENT MAINTENANCE AND SETTINGS