PUMPS 517 
with a facing against which the radial facing on the balancing piston A 
runs with a small clearance. When the radial facings of the piston and 
cylinder touch one another there is a small clearance between the collars 
and the facings of the multi-collar thrust-bearing D, thus allowing the 
spindle a very small axial movement. This movement also gives a very 
small clearance between the two balancing facings mentioned above. 
When the leakage water from the periphery of the end wheel or 
runner enters from the annular chamber E to the chamber F it is not 
drained away directly, but passes between the two radial facings of the 
piston A and the cylinder C. The maximum clearance between these 
two facings is very small, and therefore only a very small quantity of 
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Fig. 827. 
water can pass into the chamber H, thus reducing the quantity which 
has to be drained away. 
In chamber F there will be a pressure which will vary with the head 
against which the pump is working, and also with the clearance between 
the piston A and the bush B, and between the piston A and the cylinder 
C. When water in the chamber F reaches a certain pressure it will 
force the runners and spindle to move in an axial direction, thus slightly 
increasing the clearance between the facings of the balancing piston and 
cylinder. The water in the chamber F will drain away through the 
increased outlet opening, and the two facings will move away from each 
other until the intensity of the pressure between them and also in the 
chamber F is so small that the thrust on the runners overcomes it, and 
brings the runners back into their first position, consequently the spindle 
will make a small reciprocating movement in an axial direction, thus 
materially helping to ensure perfect balance. 
