Pneumatic circuit problem

Could you check if the reverse motion is not blocked by some obstruction? Perhaps the air is acting but due the obstruction is not working.

No obstructions. The valve doesn't appear to shift, since that would result in air exausting from the ex. port and it doesn't. Also, I should have said that the solenoid valve has an internal pilot for the return.

Ciould you write a Cycle Sequence for the schematic that uses nomencature like "S1"for the soenoid operator and "PB1", "PB2" for the Manual valves and "P1", "P2" for the Pilot opeated valves. I would use "Mot+" for Extend and "Mot-" for Retract to indicate the Motor action.

Explain the valve positions At Rest, before the operator starts a cycle and then go throgh a cycle Step by Step showing valve position and action. I know you understand how the cycle is supposed to perform but it is not clear to me from your explanation.

Offhand it appears the Solenoid valve should be Double Solenoid Operated or ExternalAir Pilot Operated so it stays in the last position it was shifted to since it appears the problem is the Return action starts the stops almost immediately.

I would try using a stick to hold the Limit Switch on to see if the Return action would continue.

Just a thought

Here is the operating procedure:

1. Mold is sitting on table. Operator moves lever on 2-position valve (Selector) to "retract" and presses both pushbuttons. Pilot pressure shifts 3-position (D.C.) valve to retract mold mover. Mold is pulled into press. Operator releases pushbuttons, centering D.C. valve.

2. After mold cycle, Operator moves lever on Selector valve to "Extend" and presses pushbuttons. Pilot pressure shifts D.C. valve to extend mold mover. Mold is pushed out of press against hard stops. Mold rebounds into detents. This puts mold mover into compression, we it must be retracted about 1/4" to relax it.

3. Cam-operated limit switch opens and de-energises solenoid valve. Internal pilot on Solenoid valve reverses motor. Limit switch closes and re-energises valve. Operator releases pushbuttons, centering D.C. valve and stopping mold from sitting there moving 1/4" back and forth.

4. Table lifts mold as part of removing product/refilling material.

5. Operator retracts mover as in step 1.

6. When ready to mold next part, operator extends mold mover as in step 2 & 3. "Button" on mover is now in alignment with "Yoke" on mold, allowing operator to lower mold into position.

7. Go to step 1 and repeat.

Does this explain adequately?

I see now that the solenoid valve will not reverse the motor, but that's not the main problem. It also prevents us from retracting with the selector valve. By the way, I cannot reverse the motor with the pilots for the D.C. valve; it's not precise enough (moves about 2 in after releasing the pushbuttons).

The switch is inaccessible, but we removed the pigtail and plugged into another switch which we actuated by hand. It stops the mold, but will not allow reversing it.

I am still having problems with the explanation of the desired cycle sequence and visulizing what is taking place during the cycle that does not operate as required. A big part of my problem is not being able to visualize the mechanism and the layout of the components.

Due to the compressibility of air it is difficult to get even close to precise movements especially if the motion is not greatly retarded. It appears you are using the Solenoid valve to try to make the action faster by reducing the ehaust flow path at the Motor port in the Insert direction. I have always had better control by using a 3-Position valve with the Motor Ports connected to atmosphere in the center condition so the air is not trapped but exhaust's quickly when the valve centers. Taooed air can continue to make an actuator move until pressure reduces below running force requirement.

Can you get any help from the supplier of the components? For all the years I was in sales a big part of the job was designing circuits and assisting in getting them to operate as requested. Didn't sell much just traded circuit design for an order.

Then again, maybe someone else on the forum might have some answers.

I designed the circuit, then couldn't find one of the valves I needed, so I made a change, then another change, and another and ended up with a circuit that won't do what I want. What I could do is put another 4-way, 2 position valve in with a solenoid to reverse the motor on actuation. I'd like a simpler, or at least less expensive, way. To avoid compressibility problems, I have lines to the motor that are 12" or less and would like to mount something directly on the motor. Obviously, that won't work if I use a 4-way valve. The slow reaction of the main direction control is due, I think, to long (6') pilot lines from the manual 2-position selector valve.

I have to log in at home, but not at work. I'm at home, and forgot. This was my response.

Well, your pneumatic circuit is correct. And as you said the circuit works satisfactorily while in test bench & also there is no problem in the solenoid coil. This leaves me with only one doubt - The input presuure to which your solenoid valve is connected.

The solenoid valve work satisfactorily (with properly working solenoid) only when the input pressure is above 1.8 or 2 bar. If it is less than that then the solenoid won't work. There is possibility that your test setup is giving sufficient pressure but in actual application the pressure may be less.

In such case you better try with external pilot on the same valve.

Hi HarryBurt:

As I see it in your circuit after a successful retraction the limit switch is still engaged.

Upon selecting the extension and pushing the two push buttons the mold will move but only until the limit switch is disengaged then the solenoid will de-energize and the last valve before the motor will return to its rest position which will shut off the flow of air to your motor.

I hope this helps

mechtech

If the cam swich is sticking or ingaged in any way, the 3-way 2-pos sol. valve can not exhaust and hence the circuit will be locked preventing the motor from moving. Always consider that exhaust flow rate of this 3/2 sol valve relative may be is too small and does not allow the exhasut air to flow fast enough. Try using a 1/2" or larger valve here. You make also want to look at how your transfer mechanism dis-engages with the cam switch. Based on your description, it sound like to cam swich is not de-activating...

Hopefully all of our collective suggestions will lead to a positive solution for you.

I found the problem. In revising the original, I went from a circuit that would almost work to one that cannot. I need to add a second 4-way valve to reverse the existing one. The 3-way can only stop it.

Thank you all. Responding to your comments showed me where my stupid error was.