Control Valve
Application
Guide
Nelson Irrigation Corp. 848 Airport Rd. Walla Walla, WA 99362-2271 USA Tel: 509.525.7660 Fax: 509.525.7907 E-mail: [email protected] Web site: www.nelsonirrigation.com
4.3 PRESSURE CONTROL SENSITIVITY AND ADJUSTMENT
The Nelson 800 Series pressure
control is designed with a sensitivity
response bushing which can be easily
changed to give the valve different
sensitivity. A change in sensitivity is
useful in solving pressure cycling
problems. The drawing in Figure 5
shows the location and options of
these bushings. A convenient
calibrated scale is provided on the
adjustment stem. The scale is useful
for approx-imate pressure setting. It
is always recommended that an
accurate pressure gauge be used on the valve to set the exact pressure needed. The RED bushing can be used for very accurate
pressure control on drip systems. See Section 2.4.3 and also Appendix A for details on the Nelson pressure control accuracy.
4.4 FILTRATION OF THE CONTROL CIRCUIT WATER
Filtering the water for the pressure control, solenoid and other control components is
needed for reliable operation. The internal filter provides some self cleaning and the
external filter has the advantage of being cleaned while the system is operating. See
Appendix B for a comparison and discussion of the internal and external filter options.
See Table 3 for the water volume required to fully open or close valve.
CAUTION! Water sources containing excessive debris should have some filtration.
Figure 5
(Nelson Pressure Control)
HOW PRESSURE CONTROL WORKS
11
PRESSURE
SUSTAINING/RELIEF
CONTROL
Pressure lower
than control set point
The pressure sustaining control is temporarily
out of balance. The sleeve chamber pressure
is opened to upstream pressure until the set
point is reached.
Pressure same as
control set point
The pressure control is in balance.
Pressure higher
than control set point
The pressure sustaining control is temporarily
out of balance. The sleeve chamber pressure
is opened to vent to the atmosphere valve
opens more.
WATER VOLUME REQUIRED TO
FULLY OPEN OR CLOSE VALVE
8"
4 quarts
6"
2 quarts
4"
1 pint
3"
1 cup
2"
5 oz. (145ml)
Table 3
