5 Key Factors You Need to Know to Select the Right Hydraulic Valve
Selecting the right valve for your hydraulic system is rarely an easy task. Most of us want to be able to install the valve and then only think about it when it’s time for maintenance. Understanding the factors you need to consider when selecting the valve is the best way to make sure you don’t have problems once it’s installed.
The following are the key factors for selecting the right hydraulic valve for your high-pressure water system.
1. Open-Ended vs. Closed-Loop
Opened-ended systems and closed-loop systems operate at pressures between 1,000 and 5,000 psi. Descaling is an example of an open-ended system as it involves high-pressure spraying of water (or other flow media) to perform a process. In this case it’s for steel descaling. Closed-loop systems the low-viscosity fluid stays in the system so that hydraulic pressure is converted into mechanical power to move a cylinder, turn a gear, etc.
2. System Design Parameters
Engineers need to know exactly what the system is being designed to do. Some of the parameters you’ll need to know are specific to open or closed systems, but knowing the following are important for the type of valve you’ll need:
- Required tonnage of the press (closed-loop)
- Required flow rate (open-ended)
- Velocity (open-ended)
- Consistency of flow media (open-ended)
- System pressure (both)
- Cycle frequency (both)
- Operating temperature (both)
- Pressure drop (both)
3. Flow Media
Knowing the flow media is important and can help determine the type of valve you should use. If it’s water, the cleanliness of the water is relevant. It’s not as much of an issue for closed-loop systems as it’s harder for contaminants to enter the system, but open-ended systems can collect sand or scale particles that can cause valves and its components to wear out faster.
Water hammer is also a potential problem. Water hammer is a pressure wave caused by instant changes in fluid velocity when a valve is suddenly opened or closed. It can cause pipes to burst or to pull from their anchor point, and even cause valves to explode! Certain valves are designed to limit water, but none more so than Hunt Valve’s Proportional Poppet Valve.
4. Plunger Valve vs. Poppet Valve
When choosing the actual type of valve, it mainly comes down to a plunger or poppet valve. The main difference between the two is the method in which the valve functions. In a poppet valve, a cone- or ball-shaped plug is held in place on the valve seat by a bias spring or hydraulic piston. When the plug is moved, fluid can flow through the valve.
A plunger valve is like a piston and rod in which the rod moves in and out of the hydraulic cylinder. A hollow rod with radial ports moves back and forth with the position of the ports controlling the flow of the liquid. The rod seal keeps the fluid from leaking out.
Some of the main factors that determine which is the better choice is whether you’re designing a directional control or descaling system or if your system tends to be dirty or clean. Poppet valves tend to work better for directional control and cleaner systems. Plunger valves are better used in dirtier, descaling systems.
5. Valve Configurations
Finally, the type of configuration that will work best for your high-pressure application determines the right valve style. Here are your main options:
- Isolation: The purpose of the isolation valve is to either allow or shut off flow.
- Directional Control: These valves extend and retract hydraulic cylinders such as those typically used in a forging press.
- Pump Bypass: In most high-pressure water hydraulic systems, the pump needs to run continually. Pump bypass valves are ported to direct water back to the flume or reservoir to recirculate through the pump when there is no system demand, so that that the pump does not overheat.
- Check: Because flow in a check valve can only flow in one direction, it prevents flow back into the circuit that is caused by multiple pump sources of pressure.
- Prefill: Used to reduce water hammer and damage to the upper header nozzles, prefill valves allow the filling of a system header with low pressure water from an external low-pressure source or with system pressure when used in conjunction with a pressure breakdown orifice.
- Safety: Safety valves are typically poppet style and are installed in circuits to prevent system overpressure. When the valve detects a pressure greater than the set limit, flow is directed to a relief port.
Understanding these factors will help you select the right valve for your hydraulic system. There are other things you need to know when designing the system. These include the materials to use in your valve, how to maintain the valve to avoid damage and how to prevent leakage.
Download our free guide, High Pressure Water Valve Selection & Maintenance Handbook, to learn more about each of these topics.