Asking “what is a hydraulic valve?” is like asking “how long is a piece of string?” The range of options available to hydraulic designers is staggering, not only due to the sheer variety of valve types on the market but also because of the numerous manufacturers producing them.
At its core, an Automotive Lift Repair Florida valve is a mechanical device that opens and closes, typically to regulate the flow of fluid—be it liquid or air. Valves are ubiquitous across industries, from automobile engines to the foundries that produce engine valves; in fact, there are valves on the machines that make valves.
This discussion isn’t about the poppet valves in a 1999 Civic SI VTEC. We’re focusing on hydraulic valves, which are distinctive because they must endure fluid pressures of 3,000 psi or more. Consequently, they’re often constructed from strong, heavy materials like steel and iron. These valves must be designed to contain hydraulic pressure completely, while still functioning smoothly and accurately under the high forces exerted by the pressurized fluid.
In essence, an Automotive Lift Repair Florida hydraulic valve is a device that opens and closes to control the flow that moves actuators and loads. While this might sound simple, there are various techniques in hydraulics to achieve this. Valves can be operated mechanically (via handle, knob, or cam), electrically through solenoids, or through pilot operation (using air or hydraulic pressure to actuate the valve). Some valves even use the pressure within the circuit’s fluid to actuate themselves, such as relief valves. Additionally, valves can be operated using cables, levers, plungers, torque motors, and more.
There are almost as many types of hydraulic valves as there are methods to actuate them. The three primary categories include solenoid valves, flow control valves, and pressure control valves, each with its own subtypes. Solenoid valves, for instance, can be poppet or spool types, and either can be electro-proportional or servo-controlled.
Automotive Lift Repair Florida Pressure control valves are the most diverse of the three main categories. They open and close like other valves but do so in a more dynamic way, with linear performance changes based on the pressure they experience. Most pressure valves, such as relief valves, sequence valves, and counterbalance valves, are normally closed, requiring a rise in pressure to open. However, the pressure-reducing valve is unique in that it closes when pressure exceeds a set point.
The array of hydraulic valves available is vast, and each type could easily fill its own discussion. Simplifying the complex topic of “what is a hydraulic valve?” isn’t easy, but if you understand that they are devices designed to open and close to regulate the pressure, flow, and direction of fluid in a hydraulic system, then you have grasped the basics.
Pressure-control valves are integral to nearly every hydraulic system, performing various essential functions. They help maintain system pressures below a set upper limit and ensure consistent pressure in specific parts of a circuit.
Relief Valves
Most fluid power systems are designed to operate within a specific pressure range, determined by the forces the system’s actuators need to generate to perform their tasks. Without controlling or limiting these forces, the fluid power components—and the costly equipment—could suffer damage. Relief valves prevent this by acting as safety devices that limit the maximum pressure in a system by diverting excess oil when pressures become too high.
Cracking Pressure and Pressure Override
The point at which a relief valve first opens to allow fluid flow is known as the cracking pressure. When the valve allows its full rated flow, it is at full-flow pressure. The difference between full-flow and cracking pressure is often referred to as pressure differential or pressure override.
Direct-Acting Relief Valves
An Automotive Lift Repair Florida direct-acting relief valve typically consists of a poppet or ball exposed to system pressure on one side and opposed by a spring of preset force on the other. In an adjustable, normally closed relief valve), the spring force exceeds the system pressure acting on the ball or poppet, keeping it tightly seated. A reservoir port on the spring side returns leakage fluid to the tank.
When the system pressure begins to exceed the valve spring setting, the fluid unseats the ball or poppet, allowing a controlled amount of fluid to bypass to the reservoir, maintaining system pressure at the valve’s setting. The spring re-seats the ball or poppet when enough fluid has been released (bypassed) to lower system pressure below the valve spring setting.
Most relief valves are adjustable, usually with an adjusting screw that compresses or decompresses the spring. This allows the operator to set the valve to open at any pressure within a desired range.
Pilot-Operated Relief Valves
These Automotive Lift Repair Florida valves operate in two stages: a pilot stage, consisting of a small, spring-biased relief valve (usually built into the main valve), acts as a trigger to control the main relief valve. The pilot can also be located remotely and connected to the main valve via pipe or tubing.
The main relief valve remains closed when the inlet pressure is below the main valve spring setting. Orifice B in the main valve allows system pressure to act on a larger area on the spring side of the poppet, so the combined force of this pressure and the main spring keeps the poppet seated. At this time, the pilot valve is also closed. Pressure in passage B matches system pressure and remains below the pilot valve spring setting.
Because these Automotive Lift Repair Florida valves only start opening when the system reaches 90% of full pressure, they help maintain system efficiency by releasing less oil. They are ideal for high-pressure, high-volume applications. While their operation is slower than direct-acting relief valves, pilot-operated relief valves maintain a more constant pressure in the system while relieving.
Pressure-Reducing Valves
Automotive Lift Repair Florida Pressure-reducing valves are the most practical components for maintaining secondary, lower pressure in a hydraulic system. These normally open, 2-way valves close when exposed to sufficient downstream pressure. There are two types: direct-acting and pilot-operated.