Slip-in cartridges have a two-piece construction: The insert slips into the manifold, and a control cover gets bolted onto the surface over the insert to hold it in place. The cover incorporates all the pilot flows and functions that control the poppet inside the insert and behaves as a main stage for the valve. Different inserts and covers serve different hydraulic functions. When designing a relief (or other type of function), the designer must pick a matching relief insert and relief cover.

Atop the cartridge valve cover is a D03 or D05 interface. It allows for sophisticated control of each poppet underneath via specialized D03 and D05 sandwich valves. Building a sandwich control stack for each cartridge requires caution when applying standard 10-gpm D03 valves as pilot control valves for 0.25- to 0.5-gpm cartridge covers. By adding a proportional pilot valve to the cover, the main-stage poppet turns into an electro-proportional valve.

A drawing of slip-in cartridge valves typically shows the insert and cover as separate symbols. Any sandwich valve symbols can be added on top of the cover.

Thanks to the powerful modularity of slip-in cartridge valves, each sub-function can have a dedicated and optimized cartridge, and pilot functions can be controlled modularly from the main stage. Once again, the slip-in cartridge valves’ two-piece construction makes this possible. One exception is a valve that includes a poppet position sensor. For example, a proportional flow-control poppet cartridge valve typically has one-piece construction and one symbol in a circuit.

A slip-in cartridge fits into a pocket; common pocket sizes are NG16, NG25, NG32, NG40, NG50, and NG63. NG80 and NG100 sizes are less common, and they require extra attention. Although it’s easy to use an NG80 or NG100 valve, manifold manufacturing capabilities tend to be limited for these valve sizes, and lead times on components can be surprisingly long. When drawing up the circuit, it’s helpful to label the port on the insert and the pilot-control ports on the cover.

When selecting a slip-in cartridge valve, understand that a valve’s flow rating is based on flow of a specific fluid at a specific temperature that produces a specific pressure drop. Although valves are typically rated at 5 bar, this does not mean a valve can’t pass higher flow — it will just have a higher ∆P. Still, caution should be exercised when greater flows pass through the valve.

Screw-ins can be shoo-ins

Screw-in cartridge valves screw into threaded cavities and represent a mix between poppet- and spool-type construction. A two-port cavity can accommodate many different types of valves. For example, a C-10-2 cavity can hold a check or relief, or directional cartridge. Other cavities accommodate different valves. Screw-in cartridge valves have single-cage, or one-piece, construction.

Because their capacity starts at very low flows, screw-in cartridges are available as both direct acting and pilot operated. But unlike their slip-in counterparts, pilot-operated screw-in cartridges are self-contained units.

You do not need to match pilot and main stage functions with screw-in cartridge valves. Screw-in cartridge-valves are available in many configurations and with many options, so designers must search through pages and pages of source material to find a specific built-up configuration. After purchase, some screw-in cartridge parts may come in pieces that need to be assembled. For instance, an ac or dc solenoid may ship separately from the valve body.

Two-port screw-in valve cartridges that function like slip-in cartridges are called logic valves. Screw-in cartridges are complete valves for functions, so there’s some duplicity in calling out other valve functions. For example, one manufacturer may identify a specific screw-in cartridge as a counterbalance valve, while another manufacturer refers to it as over-center valve.

Construction of screw-in cartridges often takes the form of multi-port valves. Three-, four-, five-, and six-port valves are common for directional functions. Symbolically, they look like line-mounted spool valves. However, they’re held in a cage that’s screwed into a cavity in a manifold instead of being line mounted. Screw-in cartridges are inexpensive and used extensively in mobile equipment. They have a much smaller footprint than their slip-in cousins, lending themselves to a much more compact manifold. If the valve can handle the flow and pressure, and life expectancy is reasonable, then screw-in cartridge valves become the lowest-cost option. The historical catch, though, has been the cost, time, and risk associated with errors in manifold design, which has drastically changed.

When designing circuits that lend themselves to the screw-in cartridge strengths, line mounted D03, D05 directional and proportional valves often will be used due to pressure ratings, duty cycles, or the unavailability of a screw-in cartridge product or spool type from the vendor. Screw-in cartridges are compelling for lower flows, while multiple slip-in cartridges work better for higher flows.