6 Reference and Specification
K0443 Revision A 6 - 2 [EN] English
Supply contamination
Supplies may need the removal of water, oil or particulate contamination. Any water in the
compressed gas supply will be in vapour form, i.e. non-condensing and must be removed
using a mist filter.
Oil must be completely removed
as this causes a rapid deterioration of the control valve
performance.
The compressed gas supply must not contain particulates and must be removed using a
particulate filter. Do not use a compressed gas supply containing corrosive material.
Systems without a negative supply
Without a negative supply (vacuum pump), release the positive pressure from the system to
atmosphere through the negative supply port.
The release from the negative port must be piped away to where the discharge causes no
disturbance or hazard. A diffuser may be fitted to the negative supply port to diffuse air flow.
The need for a negative supply (for optimum performance)
General
Supply pressures (at least 110% of range but less than the MWP) there must be a difference
of 10% of full-scale between the supply pressure and the maximum output pressure. When
operating at positive or negative full-scale, there must be a pressure difference between
supply and output to cause a gas flow.
Operating near atmospheric pressure or below
Any controller operating near atmospheric pressure or below requires a vacuum pump or
other negative supply connected to the negative supply port for optimum performance.
Without a vacuum supply, as the output pressure approaches atmospheric pressure, the
differential pressure approaches zero resulting in a reduced flow to the output.
Reduced flow causes an increase in the time to control to atmosphere, especially with large
user volumes, and an increased overshoot at low pressures, (Ref: Installation, Section 2,
figures 2-4, 2-5 and 2-6).
Vacuum Pump
Each PACE Control Module has a vacuum sensor. Connect a vacuum pump to the -ve supply
port. The higher the flow rate of the vacuum pump the better the PACE control performance.
Low pressure ranges <700mbar require vacuum regulation or the use of the negative gauge
pressure generator IO-NEG-G-GEN-1 option.
Conclusion
Use a vacuum supply for: A vacuum supply improves:
Absolute ranges.
Time to reduce system pressure at pressures below 2 bar (30 psi),
full-scale.
Negative gauge ranges. Control stability near atmospheric pressure.
Overshoot at low pressures.
To improve performance at or near gauge zero.
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