Danfoss APP 1.0 Installation, Operation And Maintenance Manual page 61

Instruction
6. Typical signs of wear
6.1 Valve plate
Picture 1
Picture 2
Scratches
Picture 3
Trouble shooting guide for APP pumps
180R9262 / IOM APP 0.6-1.0 Appendices - v02 / 12.2012
A normally worn valve plate has no marks/scratches but only a slightly
polished surface.
No scratches or marks should be felt. The surface must be flat and level.
A worn valve plate has scratches, and/or a polished surface. Even small
scratches will give a loss of flow.
A good way to identify a worn valve plate is to hold a straight knife edge
over the valve plate. When holding it up to the light, it will be possible to
see any space between the knife edge and the valve plate. See picture 3.
If any light can be seen between the two arrows on the picture, the valve
plate is worn.
If any scratches or marks can be felt by running a fingernail over the surface,
the valve plate is worn.
The valve plate on picture 3 is highly damaged.
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