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Poor PCU Spin/Sensitivity
General
The weights floating on a clean PCU assembly will rotate freely, slowing down gradually
to a complete stop. If the rotation stops quickly, then the PCU may be dirty and require
cleaning.
Do not rotate the piston if it is dirty as permanent damage can
occur.
If the spin/sensitivity of a recently cleaned PCU deteriorates quickly, then it is likely that
the hydraulic system has become contaminated.
During the normal operation of a deadweight tester, the working fluid flows slowly
through the tiny gap between the piston and its cylinder. If the hydraulic system has
become contaminated, any particles will tend to move towards the PCU(s) and thus affect
their performance, and possibly damage them.
If this is the case, the system must be completely dismantled, thoroughly cleaned and
rebuilt before further calibration is carried out.
PCU Assembly - 10 mm
Plug the test station to prevent leakage, and open the reservoir valve. Hold the weight
carrier (1) and lift gently up and down, the piston should slide freely within its cylinder.
If any resistance greater than fluid drag or a "gritty" sensation is detected, then the PCU
must be removed and cleaned. (See Chapter 6, PCU Assembly - 10 mm Nominal
Diameter.)
PCU Assembly - 2 and 3 mm
Pressurize the system with 1 large weight so that the piston is rotating and floating
correctly. Gently push down on the rotating weight carrier (2) and release. This should
result in a smooth, "bouncing" oscillation. If the piston does not rotate or "bounce"
freely, it must be removed and cleaned. (See Chapter 6, PCU Assembly - 2 and 3 mm
Nominal Diameter.)
W Caution
Chapter 7
Fault Finding
7-1
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