Piston Unit - WIKA CPB3800 Betriebsanleitung

4. Design and function
4.3.1 Screw pump
The screw pump is bolted to the reservoir/high pressure cylinder block fastened to the
base unit. A sectioned view of the pump is shown. The rotating handwheel (C) which
GB
is operated by the spokes (D) is attached to a threaded spindle (E). The spindle is
supported in a sintered bearing (F). As the spindle (E) is rotated, it drives a non-rotating
ram (E and K) forward, the thrust being taken by a needle thrust bearing (G). The large
diameter of the ram (H) in the barrel of the pump (J) primes the pressure system and
provides the low pressure up to approximately 140 bar (2,000 lb/in²). The small diameter
of the ram (K) in the reservoir/ high pressure cylinder block provides the higher test
pressures up to 1,200 bar (16,000 lb/in2).
4.3.2 Reservoir
A liquid reservoir is provided on the top of reservoir/high pressure cylinder block.
The reservoir is provided with a translucent cover to enable the reservoir level to be
monitored. A plug in the middle of the reservoir cover to allow the reservoir to be filled
or topped up (the plug is removed whilst the pressure balance is in use). The reservoir
contains enough liquid (approximately 150 cm³) to enable normal operation of the
pressure balance to be carried out.
Low pressure ram displacement = 60 cm³
High pressure ram displacement = 10 cm³
4.3.3 Control valves
Two control valves are provided on the top of reservoir/high pressure cylinder block.
The valve mechanisms are built into the reservoir/high pressure cylinder block and they
control the flow of liquid through internal drillings in the reservoir/high pressure cylinder
block. The rear valve is referred to as valve A and is used to control the output from the
larger diameter ram of the screw pump. The front valve is referred to as valve B and is
used to control the flow of liquid to and from the reservoir.
4.3.4 Connection blocks
Pressure supply pipes from the screw pump are terminated at two pressure blocks
mounted on the base unit. The pressure blocks are fitted with threaded bosses
projecting up through the cover plate of the base unit. These threaded bosses enable
piston units to be directly screwed on to them or connections for various sizes of gauge
connections to be screwed on to them. Oil cups are fitted to the unit cover around the
threaded bosses of the connection blocks to catch any oil drips from the gauge stand
during gauge fitting and removal.

4.4 Piston unit

The piston unit of the model CPB3800 is a single range piston unit, which covers the
range up to 1,200 bar (16,000 lb/in²).
22 WIKA operating instructions model CPB3800