I am designing a Scissor lifter and I am operating my hydraulics using solenoid valve but I want my system to be ready for every possibility so what should be the backup system if my solenoid valve stops working

  • \$\begingroup\$ how are the things connected? can you share the diagram? and also the electronics you are using? \$\endgroup\$
    – User323693
    Mar 8, 2017 at 6:12
  • \$\begingroup\$ @Umar (sukanmarketing.com/blog/hydraulic/…) you can find circuitry there I just want to add some option in case of emergency or if solenoid valve stops such that the cylinder rod can be operated manually \$\endgroup\$ Mar 8, 2017 at 6:29

1 Answer 1


'Every possibility' is not a specification. It's quite difficult to allow for meteor strike for instance.

You need to decide what failure modes are permissible, and what not permissible. With a hydraulic lifter, moving is more dangerous than stopped, at least in my book. That means you should make sure it's always possible to stop the platform.

You need to decide what component failures are likely, and what unlikely. Perhaps a valve sticking open is something you want to guard against.

Stopping the lift even in the event of an open valve implies having two valves in series wherever you might use one, the likelyhood of them both sticking open is then much smaller than the failure of one.

If they are driven by the same power supply, this could be a point of common mode failure. If you think the supply sticking 'on' is a possibility you want to guard against, through a failed short output device for instance, then you need to duplicate supplies.

You can make a 'majority voting' valve with 3 parallel paths each of 2 valves in series, driven with 3 skew circuits, so (ab, bc, ca). That way, if 0 or 1 of abc is driven, the flow will be off, if 2 or 3 are driven then the flow will be on. Do you want such complexity for protecting a tiny part of your system?

For a full manual overide, a manual valve in series with the solenoid will stop the flow if it is stuck on, and a manual valve in parallel with both will operate the lift if the valve is stuck off.

  • \$\begingroup\$ thanks for replying. Actually I am a trainee Engineer in a private organization and we are developing a scissor lifter for an aircraft company for transferring of their luggage to aircraft and my boss wants me to give him some options for backup purpose that if unfortunately solenoid valve stops working then how to operate it manually \$\endgroup\$ Mar 8, 2017 at 6:36
  • \$\begingroup\$ make sure you read the industry regulations for safety of hazardous load handling systems. A hydraulic scissor lift is quite capable of killing or delivering life-changing injuries. I'd hate the thought of operating a machine that had been designed by somebody who went on a public, amateur, help forum for design advice rather than researching industry standard practice. A manual valve in series will isolate an open solenoid. A manual valve in parallel will bypass a closed solenoid. Result, full manual control. \$\endgroup\$
    – Neil_UK
    Mar 8, 2017 at 6:47
  • \$\begingroup\$ you have been very helpful and all the works that my organization is doing are after a proper research but to be frank I have just started working here and my boss want to know what are the possible solutions I can provide him without knowing what they are actually going to do so it is time to give him response that can I would say impress him \$\endgroup\$ Mar 8, 2017 at 7:06
  • \$\begingroup\$ Never trust a software interlock to do the job of a hardware failsafe. Otherwise you're just designing a new Therac 25 \$\endgroup\$ Mar 9, 2017 at 18:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.