Chapter Two: Installation Gas Pressure and Control
15
Gas Pressure and Control
Pressure Limits
The control valve, enclosed in the 640B Series controller, is rated for a maximum inlet pressure
of 150 psig for orifice sizes A through 4; 30 psig for orifice sizes 5 and 6. For more information
refer to Applications with a Large Differential Pressure, page 40.
The control valve is not a positive shutoff valve. Some leakage across the valve may occur.
Refer to Appendix A: Product Specifications, page 51, for the leak integrity specifications. If
necessary, install a separate positive shutoff valve in your system.
Caution
Take care not to expose the transducer to pressures above its full-
scale range. Pressures exceeding 45 psia or twice the full-scale
pressure (whichever is greater) may damage the transducer.
Installing the Unit
The 640B Series Pressure Controller can be mounted to provide either upstream or downstream
pressure control. Your application determines how to mount the unit into the pressure system.
Connect the port labeled “Controlled Pressure Port” to the system whose pressure you need to
control.
Note
MKS defines “upstream” and “downstream” control by the location of the
controlled volume relative to the 640B Series Pressure Controller.
Downstream Pressure Control
Downstream pressure control occurs when the 640B Series controller is positioned before the
controlled pressure volume in the gas flow path, so that the controlled volume is downstream of
the 640B Series controller. The gas flow enters the 640B Series controller on the valve side,
opposite the “Controlled Pressure Port.” Figure 1, page 16 shows the gas flow for downstream
control.
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