Johnson Controls Tyco PRV-1A - Operation; Design Considerations

TFP1581
Page 7 of 14
Operation
With reference to Figure 4, the system
water supply pressure from the inlet
cavity of the Model PRV-1
A Valve enters
the Diaphragm Chamber through a
Strainer.
Exit ow from the Diaphragm Chamber
through the Pilot Valve is controlled by
a regulating spring that is factory set,
and subsequently eld adjustable, to
the desired downstream “set pressure”
that is to be maintained. A sensing line
connects the outlet of the Pilot Valve to
the system piping downstream of the
Model PRV-1
A Valve via the Pressure
Sensor Insert in the outlet cavity.
When the downstream pressure rises
above the “set pressure” of the spring,
exit ow from the Diaphragm Chamber
through the Pilot Valve to the Model
PRV-1
A Valve outlet cavity is stopped
and pressure increases in the Dia-
phragm Chamber. When downstream
pressure falls below the “set pressure”
of the spring, exit ow from the Dia-
phragm Chamber through the Pilot
Valve to the Model PRV-1
A Valve outlet
cavity resumes and pressure in the Dia-
phragm Chamber decreases.
The regulated ow through the Pilot
Valve decreases and increases the
pressure in the diaphragm chamber to
sufciently open and close the Model
PRV-1
A Valve, as required, to regulate
the downstream “set pressure”.
The operation sequence is as follows:
• When there is no ow demand down-
stream of the Model PRV-1
A Valve,
the Seat is closed and the Pilot Valve
Seat is closed. With the Pilot Valve
Seat closed, pressure is trapped in
the Diaphragm Chamber to seat the
Diaphragm and the Model PRV-1
A
Valve remains closed.
• When there is a ow demand down-
stream of the Model PRV-1
A Valve
and the outlet pressure drops below
the “set pressure”, the Pilot Valve
Seat opens to relieve pressure from
the Diaphragm Chamber allowing the
Model PRV-1
A Valve to open.
• As the flow demand continues
downstream of the Model PRV-1
A
Valve and the “set pressure” is met,
the Pilot Valve Seat closes. As the
Pilot Valve Seat closes to reduce
the opening, pressure is trapped in
the Diaphragm Chamber at a point
that allows the Diaphragm to remain
lifted from the Model PRV-1
A Valve
Seat to retain the downstream “set
pressure”.
• Should the downstream pressure
start to fall below the “set pressure”,
the Pilot Valve Seat re-opens to allow
for a decrease in pressure in the Dia-
phragm Chamber to allow the Model
PRV-1
A Valve to open further and
then once again establish the down-
stream “set pressure”.
• When the downstream pressure is
at or above the “set pressure” and
assuming there is a ow demand
downstream of the Model PRV-1
A
Valve, the Pilot Valve Seat is closed
to trap a sufcient pressure in the
Diaphragm Chamber to allow the
Model PRV-1
A Valve to remain open
to provide the “set pressure”.
Design
Considerations
The following items must be consid-
ered and applied accordingly for an
installation that will be using the Model
PRV-1
A Pressure Reducing Valve:
• When planning the positioning of
the Model PRV-1
A Valve, it is rec-
ommended that consideration be
given to the viewing of the pressure
gauges. Consideration should also
be given to positioning the Model
PRV-1
A Valve so that the diaphragm
cover is facing up. With the cover
facing up, internal access is more
easily achieved.
• The Model PRV-1
A Valve must be in
an area that is easily accessible for
maintenance purposes, not subject
to freezing temperatures, and not
subject to physical damage.
• The valve is designed for fresh water
service. When corrosive atmo-
spheres and/or contaminated water
supplies are present, it is the owner’s
responsibility to verify compatibility
with the pressure reducing valve,
pilot valve, and trim.
• The difference between the water
supply pressure and the desired
outlet (downstream) pressure must
be 25 psi (1,7 bar) or greater per its
FM Approval or 50 psi (3,4 bar) or
greater per its UL Listing. The differ-
ential maintains accuracy control of
the discharging pressure over the full
rated flowing range.
• Cavitation may occur when the inlet
pressure is greater than twice the
“set pressure”. For this case, the
pressure should be reduced in two
steps by using two Model PRV-1
A
Valves in series.
• When reducing pressure for a sprin-
kler system, a 3/4 in. (DN15) or larger
pressure relief valve shall be located
downstream of the Model PRV-1
A
Valve. The pressure relief valve shall
be set at a pressure 10 psi (0,7 bar)
lower than the pressure rating of the
lowest pressure rated component
down stream of the Model PRV-1
A
Valve.
• When reducing pressure for a sprin-
kler system, a listed indicating valve
shall be provided on the inlet side of
the Model PRV-1
A Valve.
• When reducing pressure for a sprin-
kler system, means shall be provided
downstream of the Model PRV-1
A
Valve to facilitate a flow test at the
sprinkler system demand.