NZ/NZ-M and NZOS/NZOS-M Series
5
Type NZ pilot-operated pressure regulator uses inlet pressure as the operating medium and reduces it through pilot
operation to load the actuator diaphragm. The loading pressure can regulate the outlet pressure by moving the sleeve
towards or away from the seat.
Any change in the outlet pressure can alter the balance of the outlet pressure and the control spring in the second stage
of pilot. The pilot diaphragm is between the outlet pressure chamber and the spring. When outlet pressure decreases,
the spring pushes the diaphragm downwards. The diaphragm moves the pilot disk away from the orifice increasing
the loading pressure. The loading pressure pushes the main diaphragm up, increasing the distance between the seat
and the sleeve. This movement allows more flow to pass through the main valve’s orifice. When the outlet pressure
increases, the pilot reduces the loading pressure, moving the sleeve closer to the seat. The flow rate passing through
the main valve decreases and maintains the desired pressure at the outlet.
Monitoring Systems
Monitoring regulation is overpressure protection by containment; therefore, there is no relief valve to continuously
vent gas to the atmosphere. When the working regulator fails to control the pressure, a monitor regulator installed in
series, which has been sensing the downstream and control pressure, goes into operation to maintain the downstream
pressure at a slightly higher than normal pressure. During an overpressure situation, monitoring keeps the fluid gas in
line. Also, testing is relatively easy and safe. To perform a periodic test on a monitoring regulator, increase the outlet set
pressure of the working regulator and watch the outlet pressure to determine if the monitoring regulator takes over at
the appropriate outlet pressure.
Wide-Open Monitoring Systems
There are two types of wide-open monitoring systems: upstream and downstream. The difference between upstream
and downstream monitoring is that the functions of the regulators are reversed. Systems can be changed from
upstream to downstream monitoring and vice-versa, by simply reversing the setpoints of the two regulators. The
decision to use either an upstream or downstream monitoring system is largely a matter of personal preference or
company policy.
In normal operation of a wide-open configuration, the working regulator controls the system’s outlet pressure. With
a higher outlet pressure setting, the monitor regulator senses a pressure lower than its setpoint and tries to increase
outlet pressure by going wide-open. If the working regulator fails, the monitoring regulator assumes control and holds
the outlet pressure at its outlet pressure setting.
Table 3.
Minimum Differential Pressure
SERIES
MAIN VALVE BODY SIZE
PRESSURE
RATING
MINIMUM DIFFERENTIAL
START OPEN
FULL OPEN
DN
NPS
bar
psi
bar
psi
NZ
25
1
ANSI 150
0.5
7.25
0.8
11.6
ANSI 300
ANSI 600
1.2
17.4
2
29
50
2
ANSI 150
0.5
7.25
0.8
11.6
ANSI 300
ANSI 600
1.2
17.4
2
29
80
3
ANSI 150
1.2
17.4
2
29
ANSI 300
ANSI 600
1.5
21.75
2.5
36.25
100
4
ANSI 150
1.2
17.4
2
29
ANSI 300
ANSI 600
1.5
21.75
2.5
36.25
150
6
ANSI 150
1.5
21.75
2
29
ANSI 300
ANSI 600
1.8
26.1
2.5
36.25
3.
Principle of Operation