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
MR/MRDC
MDC Guide
PRESSURE FACTS
6
6
5.4 MINIMAL REQUIRED PRESSURE INPUT
The performance curves show the resulting outlet pressure for several rates of flow. The reason to be
concerned about pressure loss is to know the minimum pressure required by the regulator to operate. On
the MR the desired condition is on the flat portion of the performance curve. On the MRDC, always maintain
5 PSI above the rated pressure to have the best performance. The MRDC has a unique characteristic that
requires adequate pressure to open. The regulator then maintains the correct outlet pressure as long as the
necessary inlet pressure is provided. During transition (
in-between check and regulation
) the MRDC is partially
open. Within this transition a lower than wanted outlet pressure and turbulence will result. The sprinkler may
operate but at a very low pressure that could result in poor water distribution! A partially opened MRDC
regulator can cause severe distortion of the stream and a poor sprinkler distribution pattern.
BE ALERT TO PRESSURE EFFECT UPON THE DRAIN CHECK!
Another unique feature about the MRDC is the difference in opening and closing. The graph shows
performance depending upon if the pressure is increasing (green line) or decreasing (red line). When pressure
is decreasing (like when a pump stops), the check shuts-off at a lower pressure than it opened. It is typical
that sprinklers for the next irrigation
set are turned on before the last
set sprinklers are turned off. Thus
the output will follow the increasing
pressure performance line.
The graph for the MDC performance
is shown here. The red means that
the drain check is closed. Notice that
there is a transition area between
closed and fully open. Inlet pressure
must be available to stay above the
transition area.
SOLUTION:
The solution is to always
provide the necessary pressure to the
MRDC and MDC.
CAUTION:
Do not operate at a
pressure lower than the minimum
inlet pressure.
EXAMPLE:
The 50 PSI MRDC should
be operated at 55 PSI minimum
inlet pressure to stay well above the
check-transition zone.
3.0
2.0
INLET PRESSURE (PSI)
normal #16 nozzle
regulated flow
MR regulator without check
30
40
50
60
70
check opening (increasing pressure)
check closing
(decreasing pressure)
EXAMPLE PERFORMANCE FOR 50 PSI MRDC
Flow
(GPM)
