Operation - Pressure Tech LF-792 Series Operating And Service Manual

3. Operation

Gradually turning the hand wheel clockwise compresses the load spring, which in turn
opens the main valve, and allows the inlet pressure to pass through the orifice until
the outlet pressure is equivalent to the loading forces set by the compressed spring.
Gradually increasing an air supply to the top air actuated bonnet, applies pressure
across the diaphragm, which in turn opens the main valve, and allows the inlet
pressure to pass through the orifice until the outlet pressure is equivalent to the
loading forces set by the compressed spring.
The LF-792 incorporates a segregated captured vent (1/4" NPT), which allows the
outlet pressure to be reduced whilst turning the hand wheel anti-clockwise. Excess
pressure is exhausted via the 'Vent' port marked at the bottom of the regulator and
piped to tank or other facility. Note that safe, inert gases may vent to atmosphere if
required. For Non-venting (NV) regulators, the excess pressure will not vent through
the 'Vent' Port and should be vented downstream of the regulator. Ref Section 4.
Important: The vent port should not be plugged or blocked at any time.
The LF-792 series may be offered with pressure limiting, pressure locking or pre-set
pressure options:
Pressure limited regulators are fitted with locknuts on the adjusting mechanism in
order to limit the maximum allowable downstream pressure. Regulators fitted with
pressure limiting locknuts will state the limited pressure on the regulator label and
this will also be indicated in the part number.
Pressure locking regulators are fitted with a locking cap which may be set (when
specified) to pre-determined requirements. It is secured in place by three M5 grub
screws which lock against the bonnet of the regulator creating an anti-tamper device
to ensure the pressure cannot be adjusted accidentally.
Pre-set pressure regulators are adjusted (factory set) to specified customer
requirements within a given pressure range.
Both pressure locking and pre-set pressure regulators will be fully adjustable through
a given pressure range and the maximum allowable working pressures will be
indicated on the regulator label and in the part number.
*Note - A table is available on request defining allowable tolerances for set points
within a given pressure range.
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