So you need to spec a valve. Now what?
The first step is to consider a few essential elements. What’s the purpose of the valve? What features do you need to include? Will it need to be serviced over time? How do you connect it to the system, including pipes and wires? What size should it be? When it comes to valves, there’s much to learn. For every project you take on, the key is to design with valves in mind. Read on for a primer on valve fundamentals and selecting the correct valve.
Valves: What You Need to Know
Valves are everywhere! We have valves in our hearts, in our engines, and in our showers. Put simply, a valve is a device that controls the flow through a passageway. In irrigation systems, you may see check valves, air relief valves, flush valves, master valves, isolation valves, remote control valves, and more. A valve can be described by:
- Its function in the system (e.g., a master valve or isolation valve)
- The material it’s made of (e.g., brass or plastic)
- Its operation type (e.g., manual or automatic)
- Its internal mechanism (e.g., ball valve or gate valve)
Remote Control Valves
Now that you know what valves do and what they’re made of, let’s zero in on remote control valves (RCVs). These are automatic valves that control the flow of pressurized water from a mainline into a lateral line. They often correlate to zones in your design or stations in the controller. Depending on your local codes and conventions, consider an anti-siphon valve, an inline globe or angle valve, or an index valve. Inline globe valves are the most common, especially in commercial projects where backflow is already provided at the point of connection. These devices are inline with the pipe. The water enters one side of the valve and exits through the opposite side.
Linking the Hydraulics
To function properly, a remote control valve needs to be connected to the pipe and the electrical control system, then sized properly for the demands of the system. A variety of pipes exist, but the most common are polyvinyl chloride (PVC) and high-density polyethylene (HDPE or PE) pipe. The size of the valve, measured in inches or millimeters, correlates to the size of the pipe connection. PVC systems will use a slip or threaded valve connection. The most common thread type in the U.S. is National Pipe Thread (NPT). In international markets, British Standard Pipe (BSP) is often used. It’s important to note that the two are not interchangeable. HDPE or PE systems will use a compression fitting or an adapter. Once the hydraulic side of the valve is linked, connecting the solenoid to the electrical control system is simple.
Connecting the Electrical Components
There are two basic types of solenoids: AC and DC. Use an AC solenoid when powering with 24 VAC from the controller. Use DC-latching solenoids when powering with battery- or solar-powered controllers. If you have a two-wire system, connect the solenoid to the decoder according to the manufacturer’s instructions.
Sizing the System
Sizing the valve for system demands means ensuring your valve is suited to the quality, pressure, and volume of the water supplied. If the system uses reclaimed water, opt for a valve with a more robust diaphragm and internal filters designed for this water type. If a system must withstand extremely high pressures, address this with a pressure regulator at the point of connection and a valve suited to the final operating pressure of the system. Check manufacturer specifications for the pressure rating of the specific valve. It will vary by material, manufacturer, and model. Additional pressure regulation at the valve can help provide proper pressure to the system downstream of the valve.
Valve size is based on the water volume required to supply a zone. Manufacturers provide pressure loss charts for valves based on flow rate and valve size. For proper operation of the diaphragm and components inside the valve, there must be a small amount of pressure loss, but not so much that it strains the mechanism. The desired pressure loss in an RCV ranges from 2 to 5 PSI (0.14 to 0.34 bar; 14 to 34 kPa). Valve size is never based on the size of the mainline or lateral line pipe alone. It should always be sized for the flow demands of the zone. Here’s an example: If a 2" (5 cm) mainline is supplying a 1" (2.5 cm) lateral line, but the flow demand on the 1" (2.5 cm) valve results in a 9 PSI (0.62 bar; 62 kPa) pressure loss, then upsizing the valve can reduce this loss. Conversely, if a 2" (5 cm) mainline supplying a 1" (2.5 cm) lateral is given a 2" (5 cm) valve with a 0.5 PSI (0.03 bar; 3 kPa) pressure loss, the valve is oversized and should be smaller to accommodate the zone and save on material costs.
Selecting the Valve
Irrigation design novices often think the valve is the component that decides the rest of the design. They want to know how many spray heads they can put on a valve. The truth is they’re approaching the design in the wrong order. The valve is usually the last component to be selected. You must understand the supply type and system demands before valve selection occurs. Valves are complex. Taking the time to understand the function and features of each type will help you select the proper product for your design. Be sure to consider the manufacturer’s specifications, project requirements, and zon characteristics. It also helps to know the constraints of valve operations as this will help inform the design on the front end. When you design with valves in mind, it makes selecting the right valve much easier.