Screw-In Cartridge Valves
In this lesson, we’re going to illustrate the key design elements of typical screw-in cartridge valves.
We’ll match up the manufacturer’s valve symbol and port numbering to the actual ports on the cartridge valve.
Then we will learn to interpret the information that accompanies the various valve cavity standards.
Cartridge Valves
With the advent of the milled hydraulic manifold block, it has become relatively easy to eliminate potentially leaky hose and fitting connections between hydraulic valves.
In essence, the manifold with cartridge valves is the hydraulic version of what we know in the electronics world as an integrated circuit.
Cartridge valves come in two main designs, either slip-in (which we covered in the previous lesson) or screw-in.
Screw-In Cartridge Valves
The name gives away one of the main differences from the slip-in type, which is that it has to be screwed into the manifold block.
This requires that the threads and sizing match up. Screw-in types are also not usually piloted externally and don’t require the valve cover plate like that of the slip-in types.
Screw-in cartridge valves are likely to be used with 3 port and 4 port valves where slip-in cartridge valves most often feature 2 main ports plus a pilot port.
Screw-in cartridge valves are used to build efficient, low and medium flow systems. The tiny, compact design and reduction in hoses and fittings reduces system leakage and improves responsiveness.
Types of Screw-In Cartridge Valves
Screw-in cartridge valves come as either a ball, poppet or spool valve. Each type has an application it’s best suited for. They can be used for pressure, flow, or directional control.
That's a lot of types!
Ball check valves are used for load holding, shuttle valve logic, and very simple pressure control.
These are as simple as they come, very low cost and leak-free, but they can cause pressure shocks as they close so suddenly.
Poppet valves (also known as a seated valve) are used for load holding as well as logic, directional, and some pressure control functions.
Just like ball check valves, these valves have near-zero leakage and are generally limited to valves with only 2 main ports.
The use of a spool is common for pressure reducing functions and for directional and flow control valves. The spool design often allows for more gradual opening and closing.
internal leakage.
Valves with 4 ports are usually spool valves. The downside is that spool valves are internally leaky due to the cylindrical clearance between the spool and the sleeve.
Here is an example of a 4 port, float center directional valve.
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