Even though hydraulic valves are relatively simple devices, often with only one or two moving parts, close attention needs to be paid when replacing them. Subplate-mounted solenoid-controlled valves can have a variety of spool conditions and solenoid voltage options. Even though the replacement valve may physically fit in place of the original valve, the function can be different and result in a potentially hazardous unintended movement when the machine is started. Mobile-style sectional valves not only can have different spool configurations but also multiple other options. These options can be in the individual valve sections as well as in the inlet and outlet sections. Cartridge-style valves, both the common cavity style that conforms to an ISO standard and valves that fit a proprietary cavity, can be flow control, directional control, or pressure control that fits into the same cavity. Cartridge valves may have the same mounting thread but a different cavity profile to accommodate the three or four flow paths compared to a simple two-flow path cavity. The extra paths connect to a third drain or pilot port. The same mounting thread can also fit a four-way directional valve or pressure valves with both separate drain and pilot ports with different cavity profiles.
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