Need help with a Haas smtc

We have a 1999 Haas vf-4 which decided that it did not want to complete smooth tool changes anymore. The pocket would not lock in the down position, trying to troubleshoot we have replaced all the air lines, removed the check valve on the side of the pocket piston that holds the pocket up when there is no air pressure, and replaced the solenoid. The problem has persisted.

As far as I can tell this is what is happening:

This is the air flow of the solenoid when the pocket is up.


This is how the air should be routed when the pocket is commanded down.


This is what is actually happening when the pocket is commanded down. Because we are not getting the proper pressure to the piston, the pocket action is slow and never actually locks into place.



Has anyone ever come across a problem like this? We are stumped. we can remove the coil pack from the solenoid and command the pocket up and down with the manual override and get the same behavior.

If the solenoid spool is leaking, you'll be able to hear air leak from its exhaust port when you manually actuate the solenoid's override. Now, it *could* be leaking intermittently when the solenoid coil shifts the spool versus when you manually shift the spool using the override, but that type of thing would be real hard to diagnose definitively.

Probably the most painless thing to do would be to replace the solenoid for another one and see if that takes care of it. It wouldn't be a bad idea to have it as a spare if the solenoid ends up not being the issue. Check ebay for the part number and you can probably get one for relatively cheap (like $30-50)

YdnaD said:

If the solenoid spool is leaking, you'll be able to hear air leak from its exhaust port when you manually actuate the solenoid's override. Now, it *could* be leaking intermittently when the solenoid coil shifts the spool versus when you manually shift the spool using the override, but that type of thing would be real hard to diagnose definitively.

Probably the most painless thing to do would be to replace the solenoid for another one and see if that takes care of it. It wouldn't be a bad idea to have it as a spare if the solenoid ends up not being the issue. Check ebay for the part number and you can probably get one for relatively cheap (like $30-50)

Click to expand...

We have bought 3 solenoids and they all have similar random issue. A work around that helps our problem get slightly more consistent on tool changes is. 1. Have in recovery mode with pocket down 2. Drop pressure regulator on back of machine to zero then raise it back up to 100PSI. (SOMETIMES as pressure is dropping the air valves seat and leak stops. We have run all day and pockets lock down and no leaks after that. Next morning we have same issue and do work around and be OK again for the day. Now pockets lock down randomly.) 3. Command pocket up and down in recovery mode and it is faster going up and down and randomly locks correctly down.

Frustrating because it makes no sense that doing work around should make it behave any different then it was before pressure adjusted down then back up to previous 100PSI setting.

Is it possible the issue lies in the actuation cylinder? Not the valve.
Also, should't you be closer to 85-90psi?