5/3 closed centre valve
by Peter Foster
(New Castle, Delaware)
Valve circuit schematic
We use a Festo 170248 5/3 closed centre valve to actuate a double acting cylinder.
I understand that if the air or electrical supply is interupted the cylinder will remain in position (except for some creep due to the different surface area at each end.
My question is if the valve function itself fails (spring/leak etc.) do these valves default to the centre closed position?
We are trying to answer a safety question as to what happens if something goes wrong with the valve. Thanks. I've attached the schematic, the valve in question is the one going to the DNG-200 cylinder.
I spent some time working as a territory rep for Festo, so know that if you contact them, they will have a distributor rep by to see you in no time, at least that's the way it used to be.
Having said that, the best thing to do to determine the answer to your question is to look at the schematic of the valve.
I have uploaded a copy of the Festo 170248 5/3 closed centre valve schematic, and ask you to review it. In particular, look at either end of the schematic, and note the graphic that denotes a spring.
Since there is a spring on either end, if this valve fails due to loss of electricity or air pressure, it is designed to "spring center", and in so doing, block all ports.
If there were no springs, "sticktion" would come into play, and the valve spool would likely stay in the position it was last in if the power and air disappeared, unless vibration moved the spool. That would not be a safe type of valve configuration to use.
In other words, the valve you have selected is designed to "fail safe" by blocking all ports and stoppping any actuators in the event of a power or air disruption.
Hope that helps.