Purge System Theory Of Operation; Pressure Switch & Pressure Gauge - Bennett CNG Series Installation Manual

Bennett CNG Series Installation Manual

Purge System Theory of Operation

To prevent the formation of flammable combinations, compressed natural gas systems must be purged prior to
usage. It is required for the electronic enclosure of the dispenser to maintain a minimum pressure differential of 0.15
inches of water at all times. To achieve this, a blower must be installed and attached to the port at the bottom of the
vapor barrier as shown in Figure 13.
The purge blower is used to provide a constant flow of air to the dispenser to prevent any gas from entering and/or
accumulating in the electrical enclosure. A timer & relay, Magnehelic® gauge, and pressure switch are used to control
the power of the dispenser.
Pressure Switch & Pressure Gauge
Note: The pressure switch shown in Figure 14 and gauge shown in Figure 15 are located in the hydraulics portion
of the dispenser, on Side 1.
Figure 14 - Pressure Switch
The electrical cabinet must maintain a minimum pressure differential of 0.15 inches of water column at all times. If at
any time, the pressure differential drops less than 0.15 inches of water column a switch will turn off, causing a timer
and relay to remove power from the dispenser until the pressure differential returns to at least 0.15 inches of water
column. The power will be removed immediately after the switch recognizes that the pressure differential has
dropped to less than 0.15 inches of water column.
Piping Installation
Figure 13 - Purge Blower Port (Side 2 View)
12
Blower Port
Figure 15 - Pressure Gauge
Piping Installation