Sequence valves are like the rotary telephone of hydraulic technology. If you’re in the thirty to sixty age range, you’re like, “I remember those!” If you’re older than sixty, you’re like, “I still have one of those!” If you’re younger than thirty, you’re like, “What the deuce is a rotary telephone?” Sequence valves still exist … HydraForce and Sun have at least three dozen of them available in their standard cartridge valve catalogues, yet I’ve seen as many of them at my workplace as I have rotary telephones.
I don’t want to get into too much detail on operation of the various types available, but I can tell you they’re essentially (normally closed) relief valves capable of pressure at all ports, and usually able to reverse flow…that’s about it. They usually have a drain line as well, because both work ports are often pressurized. Their function is to allow for sequential operation of a secondary actuator after pressure in the main leg rises above the sequence valve’s spring setting.
For example, a sequence valve could be used on a clamp and drill function, where a solenoid valve operates a hydraulic clamp cylinder. Once the material is clamped, pressure will rise to relief valve setting. The sequence valve pressure will be set somewhere below relief pressure, but higher than the pressure to extend the cylinder prior to clamping. To throw some numbers at you, imagine it takes 400 PSI to move the clamp, and the main relief is set to 3000 PSI, setting the sequence valve at, say, 500 PSI and above, will allow it to open to start operating the drill motor once the cylinder dead ends.
I suppose there are a hundred designers reading this whom still love a good sequence valve circuit. A sequence valve in a circuit might only cost a buck-fifty or so, but in this day and age, there is definitely a better way to do it. The first option is to just us an inexpensive pressure switch. I’m not sure electro-mechanical switches are any more reliable than hydraulics, but you can sure buy a cheap pressure switch these days. If you get a solid state piece, reliability is surely superior to the hydraulic option.
For perhaps twice the cost of a sequence valve, you can purchase a pressure transducer and smart relay combination with oodles better performance, and gads superior reliability than a counterbalance valve. Repeatability, accuracy and hysteresis will all be superior as well. The future of hydraulics contains the “electro” prefix, and besides being an economical and reliable replacement for a sequence valve, there will be few machines in the future not already utilizing electronics. I say hop on board and enjoy the ride.