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A hydraulic control valve regulates the flow of fluid to enable various types of functions within a hydraulic system. The valve is designed to adjust flow rate by adapting the rate of energy transfer. By doing so, it can reduce or increase the speed of a motor, actuator, cylinder, or other device. Similar valves are used in faucets and showers.
 
Another benefit is a hydraulic valve can depressurise part of a hydraulic circuit to, for example, allow hose fittings or other components to be changed. Changing the flow rate is the primary means of managing a control valve’s performance. There are different ways of measuring this, including volumetric flow rate (units of volume per unit time), weight flow rate (units of weight per unit time), or mass flow rate (mass per unit time).
 
Different valves serve different purposes. Therefore, one can understand the need for specific types of valves depending on the application.

Directional Control vs. Pressure Control vs. Flow Control

A directional control valve is designed to start, pause, stop, and change the direction of flow of fluids in a hydraulic system. Also called a switching valve, it is identified based on the number of working ports and spool positions (a 2/2 valve has two ports and two positions and a 4/3 has four ports and three positions). Spools can change positions within the valve body to manage fluid flow. While a simple binary valve either blocks or allows fluid flow, a three-position valve can block all ports to stop fluid, extend the cylinder, or retract it.
 
Pressure control valves release excess pressure from the hydraulic system. They have relief, reduction, sequencing, counterbalancing, and unloading functions, depending on the valve. By regulating pressure, the valve can prevent leakage. It can also help you avoid a burst pipe or tube.
 
Flow control is a function that regulates flow rate to change actuator speed. The flow rate also influences the rate of energy transfer at the achieved pressure level. Both fluids and gases can be controlled/adjusted while backflow towards components is prevented. Flow control valves come in fixed flow, adjustable flow, throttling flow, and pressure-compensated flow control models.

Types of Hydraulic Control Valves

Flow control valves help run automated processes in factories, operate warehouse equipment, and manage various systems in food processing and materials handling facilities. Numerous types have been developed to accommodate specific applications and equipment. Some common hydraulic control valve types include:

• Ball: Comparatively durable and affordable, ball valves are not as precise as other types of control valves. They are not suited for making fine adjustments. Opening and closing a ball valve requires high torque, while ‘play’ between the stem and ball prevents an operator from achieving specific flow rates. However, trunnion/v-port ball valves offer a higher degree of accuracy.
• Butterfly: A rotating disk controls flow, although this design prevents linear flow and butterfly valves don’t provide a high degree of accuracy. Operating the turning mechanism opens and closes an internal metal plate. This is an affordable, and useful, option in applications where high accuracy isn’t a priority.
• Diaphragm: A flexible, elastomeric disc connects with the seat at the top of the valve body. Forming a seal, the diaphragm transmits force in response to pressure—opening, closing, or otherwise controlling the valve. The closure element and flow stream are separated, so this type of valve is suited for use in dirty, corrosive environments, so the valve body must be made of corrosion-resistant materials. Diaphragm valves have low leakage, are easy to clean/maintain, and can be repaired without shutting a pipeline.
• Gate: Operated by rotating a stem to turn fluid flow on or off, gate valves are used in straight-line fluid flow applications that don’t require throttling. The gate moves up or down on a threaded step when the stem is turned. Its multi-turn design prevents water hammer. This design also minimises pressure loss, as gate valves usually have no obstructions in the flow path. Gate valves are suited for use with several fluids and operate over wide temperature, velocity, pressure, and flow ranges.

The two subtypes include parallel gate valves, with a flat gate placed in-between two parallel seats, and wedge-shaped valves with two inclined seats that are slightly mismatched with an inclined gate.

• Globe: Designed for linear flow applications, globe valves can start or stop a flow and regulate it. A flat or convex plug lowers onto a horizontal seat to close the valve; the plug raises to permit fluid flow. Globe valves are also used in throttling applications. Not a straight through valve, a globe type produces a higher pressure drop, so it is suited for applications where this isn’t a concern.
• Pinch: Featuring one or more flexible rubber tubes that stop flow, pinch valves are suited for liquid/slurry applications with suspended solids. The valve can close around these entrapped solids. It is actuated by placing air or hydraulic pressure directly on the sleeve, with the valve body itself functioning as an actuator. This design eliminates the need for hydraulic, pneumatic, or electric operating components.
• Needle: A needle valve controls flow volume in small lines, turning fluid at 90 degrees and directing flow through an adjustable orifice. A cone-shape-tipped rod is positioned to change the size of the orifice, while minimal force is needed to operate the finely threaded valve stem. Needle valves can be used for shut off when instruments must be installed or removed and for calibration via fine adjustments. They are used in a wide range of industries.
• Plug: Available in various configurations, a plug valve regulates flow by rotating a cylindrical or cone-shaped plug inside the valve. An eccentric plug valve incorporates a half plug; it increases seating force while minimising friction during opening or closing. An advantage is greater shut-off control.

How to Choose the Right Hydraulic Control Valve for You

Choosing a hydraulic control valve requires determining the best one for your application. In addition to type, factors to consider include the valve configuration, media type, port size/type, operating voltage, flow rate, operating pressure, and temperature range. From plumbing to aerospace, hydraulic valves are found in many applications.
 
At White House Products, Ltd., we supply a wide range of hydraulic valves from leading manufacturers. Browse our online catalog or call +44 (0)1475 742500 for help finding the product with your required specifications.