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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

3.2  SIZING PRESSURE CONTROL VALVES

To size pressure control valves, both the pressure loss and the operating conditions must be considered. Generally the

pressure control valve is only partially open. The sleeve reacts to the pressure regulator which responds to the changes in

the irrigation system pressure. To correctly size the 800 Series valve size, three things must be considered: 1) the pressure

differential, 2) the flow through the valve and 3) the expected downstream pressure.
When doing a design, determine the worst case pressure differential operation point. A large pressure differential and a

low flow condition will position the sleeve very near the center seat. This condition should be avoided. It is generally best

to select the smallest valve which will work.
If cavitation occurs it could cause wear and deterioration of the valve parts. Nelson Irrigation can make no guarantee that

the valve will work under all conditions because of the many variables which can be encountered. Ongoing tests are being

conducted at this time to exactly identify the areas of operation that are safe. Each valve style has unique performance.

Contact the Nelson Irrigation factory for the latest test results and information on the valves.

A NOTE OF CAUTION:

 Significant fluctuation of pressure can be a problem in some hydraulic systems if a cyclic pressure

wave develops. Abrupt pressure change or flow change is a potential cause which could upset the valve. It is also possible

that extra long pipe, either upstream or downstream, or valves in series can create a condition where the regulator "hunts"

and is not stable. This condition is difficult to predict. Many times the problem can be avoided by using a 

RATE

-

OF

-

FLOW

 control slowly

filling the line or slowly changing flow rate. If the unstable situation is due to pressure control responsiveness, then see Section

4.3 or contact the Nelson factory for assistance regarding the pressure control sensitivity options available which have been

designed to solve such problems. Impeller type flowmeters cause turbulence that can affect the valve sleeve. Do not locate

flowmeter immediately upstream of the valve. If a flowmeter is to be used then it is best to locate it downstream of the valve.

4.0  UNDERSTANDING HOW THE PRESSURE CONTROL REGULATOR WORKS

The regulator used on the NELSON 800 Series Control Valve is a three-way (3-way) regulator. The regulator adjustment screw

is used to establish the pressure set point. If the pressure is higher than the internal spring then water is directed through the

regulator to change the sleeve position.
Other two-way (2-way) regulators function differently from the Nelson 3-way regulator. See the discussion on differences in

section 4.1. The following page (Section 4.2) shows in Figure 4 how the Nelson 3-way control regulator functions and the

resulting affect on the 800 Series valve under different situations.

4.1  DIFFERENCES BETWEEN 3-WAY AND 2-WAY REGULATORS

The 800 Series pressure control is a 3-way, spool-type pilot designed to serve pressure regulating purposes. The pressure

control is a self contained regulator with no external accessories needed. It works very well for both pressure reducing and

pressure sustaining or relief. While many other manufacturers use 2-way pressure control pilots that depend upon continuous

water flow through them, the 3-way pilot on the NELSON 800 Series Control Valve operates by directing very small amounts

of water in and out of the sleeve chamber.
The 3-way pilot on the NELSON 800 Series Control Valve has the following benefits:

• LOWER PRESSURE LOSS: The 3-way pilot reduces pressure loss across the valve because when turned to open; the valve

completely opens.

• LESS FILTRATION: Water moves through the controls only when there is a change in line pressure. At steady pressure

conditions, there is no water flow through the control pilot.

• SIMPLE ADJUSTMENT: Setting of the desired pressure is simple with the Nelson 3-way regulator. Only a single adjusting

screw is used and no flow control auxiliary devices are required. See Appendix A for pressure adjustment control instructions.

Due to the features of the 3-way pilot, maintenance of the NELSON 800 series pressure control pilot is minimum and many

times troubleshooting of the controls is simple and can be done with little training.

• MORE ACCURATE: The 3-way pilot on the NELSON 800 Series Control Valve has a pressure control regulator which is

extremely reliable and sensitive to slight pressure changes.

• LESS COMPLICATED: The Nelson 3-way pilot eliminates the need for flow regulating needle valves reducing maintenance

requirements. The 3-way regulator filter may never need cleaning because of the low quantity of water flow required for

the control pilot. This helps in the reliability of the entire control package!

HOW PRESSURE CONTROL WORKS

9

Summary of Contents for 800 Series

Page 1: ...800AG 4 800 SERIES CONTROL VALVES CONTROL VALVE APPLICATION GUIDE By Tom Young P E M S...

Page 2: ...alveiscontrolled byarubbersleevewhichisactuatedbyhydraulicpressure Thevalveiseitherinthefullyopenedortheclosed shutoff position The AUTO positionontheselectorhasnoeffectonvalvecontrolbutisusedwhenthev...

Page 3: ...hydraulicremotecontrolwhicheliminatestheneedforwiresinthefield Seesection2 4 2formoreinformation on the hydraulic remote function Contact the factory for specific details on the special function valve...

Page 4: ...rp 848 Airport Rd Walla Walla WA 99362 2271 USA Tel 509 525 7660 Fax 509 525 7907 E mail info nelsonirrigation com Web site www nelsonirrigation com Control Valve Application Guide Figure 2 TYPICAL CO...

Page 5: ...be removed to open the valve PRESSURE REDUCING ELECTRIC ON OFF VALVE CONTROL FUNCTION items D2 through D4 E20 through E72 on the VALVE SELECTION GUIDE The PRESSURE REDUCING ELECTRIC ON OFF model of th...

Page 6: ...ng straight pipe will help Also use of a straight pipe on the upstream end of the valve will help To be effective the upstream pipe should be a minimum five pipe diameters long 3 0 PROPER VALVE SIZING...

Page 7: ...GPM Cv Valve sizing coefficient flow rate at which one psi DP occurs NOTE Cv provides an index for comparing the capacities of different size valves The Cv coefficient is defined as the flow GPM whic...

Page 8: ...ter is to be used then it is best to locate it downstream of the valve 4 0 UNDERSTANDING HOW THE PRESSURE CONTROL REGULATOR WORKS TheregulatorusedontheNELSON800SeriesControlValveisathree way 3 way reg...

Page 9: ...e upstream water is applied to the sleeve chamber The flow is closed off by the sleeve against the center seat SOLENOID CONTROL HOW PRESSURE CONTROL WORKS 10 PRESSURE REDUCING CONTROL Pressure lower t...

Page 10: ...ering 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 advantag...

Page 11: ...n cause water hammer in the case where no valve is used Severewaterhammercancausedamagetopipes pump pressure regulators and seals The water hammer shock waves move at the speedofsoundinwater 4660ft se...

Page 12: ...ngontheamountofcurrentrequiredtooperatethecontrolleritself and the number of valves that the controller is designed to operate per station A qualified licensed electrician should be employedtoinstalla...

Page 13: ...rom controller to valve FOR VARIOUS WIRE SIZES for 24VAC solenoid OPTION E41 Inrush 1 1A Common Power Wire AWG Wire AWG 18 16 14 12 10 8 6 18 246 302 353 395 427 449 464 16 302 391 481 561 628 678 713...

Page 14: ...to the valve from the controller L 3 maximum expected line pressure on the valve solenoid 4 the allowable voltage loss AVL in the wire without affecting function of the solenoid 5 controlleroutputvol...

Page 15: ...er required to move the solenoid plunger Very low holding power is desired to reduce draw down of the batteries or storage units Two wire controls are more common and easier to purchase worldwide THRE...

Page 16: ...e dramatically with changes in flow rate The valve is close to the drip tape Choose the 5 50 PSI pressure control because it will maintain 10 PSI more accurately than the higher pressure controls Choo...

Page 17: ...H2 FEATURES Theexternalstylefilterisequippedwith a100meshscreenwhichgivesmuchgreaterfilter screen surface area than the internal filter This could mean less frequent cleaning required The screen can...

Page 18: ...n the control tube When power is off the Normally Open NO port is is connected to common The NO port is generally attached to upstream Manual selector valve Remote hydraulic relay Reducing Pressure Co...

Page 19: ...d within the working specifications for which the product was designed and under normal use and service The manufacturer assumes no responsibility for installation removal or unauthorized repair The m...

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