What is in this article?:
- Integrate control solutions using cartridge valves
- New materials, new possibilities
Valve cartridges provide only the guts or internal moving elements of the valves. A cavity in a manifold or some other machine element serves as the body.
Cartridge valves can be described as control elements that require a housing, or manifold, to unlock their full potential. They can take many forms and offer a wide range of functions from the simple fixed orifice to the most advanced proportional directional and pressure controls.
The key to unlocking the functionality of these valves comes from the innovative circuits that hydraulic circuit designers create with hydraulic integrated circuits (HICs). HIC manifolds can be used to control one or more machine functions. Practical limits can occur in packaging, but it is not uncommon to see up to a dozen functions controlled by a single HIC.
Cartridge valve elements can be thought of as "bodyless" — valves without an integral housing — because they consist of only the internal moving elements of the valves. The cartridge valve must be inserted into a cavity in a manifold and provided with appropriate flow paths to perform the proscribed function. The cavity helps define the function of the valve. Cartridge valve manufacturers design and produce valves to fit three major types of cavities: industry standard threaded cavities, slip-in cavities, and logic elements (or insert type elements).
Industry standard threaded cavities provide a threaded interface to fasten the cartridge into a manifold. The thread form is similar to an SAE threaded interface with a spot face at the mounting surface and O-ring seals for leak-free operation. The cavity has multiple steps to accommodate a particular functionality. A simple check valve requires a one-step cavity with two flow passageways. The flow paths provide passageways to the nose and sides of the cartridge. Because the cartridge valve can provide flow 360° around the its body, designers can direct flow to or from multiple sources. A more complicated functionality — such as a directional valve with three positions and four flow paths — requires a cavity with three steps and four flow passageways. Flow patterns are specific to valve manufacturers and can vary as applications require.
Slip-in valves are a relatively new form in HICs. The slip-in cartridge valve, Figure 1, was developed for use in low-pressure applications in power shift transmissions. The slip-in valve, as its name suggests, slips into the manifold and is retained with a clamping mechanism or plate that is secured on the face of the manifold.
The slip-in valve was developed to maximize the flow in a given size cartridge and typically has flow ratings equivalent to a threaded cartridge one size larger. Slip-in valves can offer lower costs when controlling pilot flows from joysticks and brake circuits. They are particularly appealing when assembling valves into complicated castings, because they create no contamination. State-of-the-art designs often incorporate slip-in valves into the hydraulic reservoirs of transmissions and engine oil pans.
Logic elements are a form of pilot operated cartridge valve, Figure 2, that are used in much the same ways as DIN style cartridges. Logic elements are capable of high flow rates and can be manufactured to much larger frame sizes than typical threaded style cartridges. Logic elements rely upon pilot flow for control and can be used as flow control elements, relief valves, and directional controls.
When used in conjunction with proportionally varied signals, these elements can be used to create multi-stage valve controls. An increasingly popular variation on the logic element is an inserted element that is placed into a machined bore and retained in the manifold with a threaded or flanged cap.
Cartridge valve manufacturers provide a wide variety of valve functions, allowing circuit designers to find almost any hydraulic control function in cartridge form. Typical functions provided by cartridge valves today include:
- check valves
- pilot-operated check valves (single-and dual-pilot operated)
- relief valves (both direct and pilot operated)
- sequence valves c pressure-reducing valves c flow control valves (pressureand non-pressure-compensated)
- load-control valves c counterbalance valves c flow-dividing/combining valves (fixed, priority, proportional divider)
- manual directional valves c solenoid valves in 2- or 3-way poppet or spool type, and 4-way, 2- or 3-position versions
- electro-proportional directional, flow, and pressure controls, and
- specialty valves: shuttle valves, velocity fuses, and composite material valves.
Innovations in cartridge valves have taken many paths in terms of functionality, size, and form. Manufacturers are incorporating multiple functionalities into single valves mixing flow, pressure, and directional controls to reduce the number of cartridges required to perform a given task. Additionally, internal valve leakage issues are being addressed with the use of engineered composites and other exotic materials.
Valves continue to grow both smaller and larger, as HICs are used to tackle lower flow applications and main system controls. Cartridge valves are being used in applications once thought to be purely the domain of sectional spool valves with capabilities beyond 50 gpm within reach. Miniaturization of valves for use in compact hydraulic packages has created valve solutions that are the thickness of a pencil and less than 1-in. long.
Pressure capabilities of cartridge valves continue to expand, as well. Demanding applications in the mobile market are pushing working pressures to 6000 psi (415 bar) with intermittent demands of up to 7200 psi (496 bar) in some cases. Cartridge valves capable of operating in these conditions and beyond are being developed and produced in many styles.
Advancements in cartridge design also come from practical areas, as machine users place equipment in more demanding environments. Some of the most important gains in machine reliability have come from improved resistance to moisture in electrical solenoids. Users — particularly in the growing rental markets — frequently wash down equipment with high pressure washers. Solenoids with molded connectors and weather resistant molding techniques offer IP69 ratings for maximum protection.