Electro-Pneumatic Valve Problem

What kind of failure? How many cycles between two successive failures ? Is it used according to manufacturer specifications ? I tried to find the valve but was not able to get it Could you indicate where the data sheet and a description is available via INTERNET ?

The performance of the valve deteriorates and hence the movement of actuators slows down.The failure is very frequent ie nearly one in 36000 cylcle.It is used according to the manufacturers specification.This is a special kind of valve used in the explosive environment.The SXE series valve is only used.

www.norgren.com/document_resources/EN/en_Atex_brochure.pdf

www.norgren.com/document_resources/EN/en_NExpress.pdf

Please guide...Thanks in advance

We had many valves fail early due to moisture in the air lines.

Exactly, same problem happens here very often.....what measures you have taken to prevent it.???

Moreover, the valve also fails due to other reasons also.......i guess......

What do Norgren have to say about it?

Your part number "SXE9561-E86-00B" is not found on the Norgren site - can you give a link to the datasheet?

Are you conditioning the air according to the specifications?

Do you have enough pilot pressure (assuming it's a piloted valve)?

Yes i also dont find the specific valve's datasheet in norgren site.

the air is compressed and dried in a air drier.It even passes through two moisture separator units before reaching the equipments.We also have a FRL unit in the equipment.

The valve is solenoid actuated 5/2 valve with spring return.It also has a manual override.In the test certificate provided by norgren, it is mentioned as

"the valve can be used with or without lubricant as it is lubricated for life long"

Since your "primary" problem appears to be moisture in the operating air- either install a desiccant dryer rated for -40F pressure dew point (normal air driers only run at about +40F pressure dew point) OR

Switch to nitrogen through a regulator- safe, simple and dry.

Since message #6 says the air is dried and filtered at least twice how the heck did you get a vote for good answer claiming that the primary problem is water?

"I" did not claim that the problem was water in the lines- the OP stated that in reply #4 as an answer to reply #3.

Before you start shooting from the hip- read the entire post.

After you made the description of the valve and mentioned that you had problems with water condensation. I dare say that your air reparation system does not work properly.

A valve as you say can loose its flow capacity ONLY if orifices are partly clogged or if an excessive friction (sticking) does not allow a full stroke of spool or if some where a deposit does not allow the full stroke.

The solenoid delivers a constant ma as long as it is not overheated, the spring can only loose preload which would not perturb the opening but only make return slower, so that the only disturbing factor can be either dirt, or oil+dirt or water condensate + dirt.

The clearance spool-bushing is very small in the range of a few micrometers for air leak limitation. Even small quantities of dirt combined with small quantities of oil can generate resistance forces big enough to stop the spool before end of stroke under normal conditions since the force on the spring will be lowered by friction.

I would put a filter in front of the valve since dirt can be present in the ducts AFTER the place where you prepare your air. The filter should be quite big and VERY fine. I think that you will already notice a better result with this simple implementation.

I would suggest you take a couple of broken down valves and disassembly with care under clean conditions in order to see what is present in side.

If the valve would have had less flow from the start it could have been possible that the flow was too important for the valve and the flow forces too big but this seems not to be the case.

2

The valve number you specified a non-cataloged, a special or modification. If you specify the operating pressure and cycle rate it would help to determine the problem.

The part number specified indicates Single Sol., External Pilot, Two position, Spring Return, Integral Speed Control. If that is what you are working with the most likely modes of failure might be.

1. Solenoid heating from very rapid cycle rate (inrush current).

2. External Pilot pressure too low.

3. Pilot exhaust plugging trapping pressure that opposes the return spring.

4. Speed Controls building contamination or frosting at very high cycle rate.

Your valve spool moves on a virtual air bearing without friction from seals. It could only operate slowly if the pilot force (pressure, or solenoid opening inadequate) or the spring force cannot overcome pilot pressure.

The cylinder and not the valve may be the problem. Which stroke in, out or both are slowed. The valve will work well without lubrication. The cylinder not so much. The cylinders will not last as long as the valve but lubrication will extend their life. Take the air lines off the cylinder and verify smooth movement. If the cylinder is not smooth or runs warm replace it and try again (with added lite lubrication).

Look for possible mechanical interference.

If cylinder is slow going forward when the valve is energized look at pilot and speed control issues.

If the cylinder is slow retracting look at pilot exhaust and speed control issues.

1. Manual over ride fully off.

2. Min. pilot supply pressure (Cat. 14.5 psig) 20 psig.

3. If pilot pressure exhaust is exposed it may contain contaminants. Clean out the pilot exhaust passage. If nothing else blow high pressure reverse flow through it.

4. If pilot exhaust is covered with a protective cap clean or replace it.

5. Take off lines to cylinders and back flow high pressure from the exhaust ports to clear possible debris.

Let's parse the statement "No added lubrication required". That means if you are willing to accept approximately half of the possible life of components the grease added at original assembly may help them last that long. Very light lubrication (no visible liquid in cylinders) will serve you right.

If all else fails buy a new valve.

I think some comments have to be made with respect to your text:

- in such pneumatic valves usually the pilot (if available since the OP specifies only a solenoid with spring return type) is using the main pressure so that the "pilot" pressure can be low ONLY if the supply orifice is not clean. But a pilot leads to an air leak which is usually not wanted so that not process valves are direct drives and do not use pilots. But even in the case of the presence of a pilot the final pressure is the main supply pressure when the spool stops so that it cannot be lower. A lower pressure can be obtained ONLY if the pilot stage is a pneumatic potentiometer and in an "on-off" valve this type of pilot is not used. If the pilot supply orifice is clogged then the spool commuting time will be longer but the main flow is the same as long as the spool makes its full stroke and the spool controlled orifices are clean.

- the OP answered that the valve is used according to manufacturer spec, the number of cycles/hour is usually indicated I doubt knowing the allowed cycling that the valve would be used at a higher cycling than permitted. What is disturbing is the VERY low number of cycles to failure. Such valves under correct conditions work several million without problems.

- I doubt that the cylinder is the culprit since by change of the valve the cycling is OK, if the cylinder would be at the origin then a valve change would NOT change the behaviour!

- A mechanical interference would NOT be generated progressively and will not be function of the valve!

- with respect to lubrication, many modern valves (we speak about the valve isn't it?) use surface treatments with anti-friction materials (for pneumatic valves only) since in many cases the process requires an oil free air either for personnel protection or because oil can pollute the product, if the manufacturer specifies "oil free" the presence of oil could harm and in stead of increasing life as you pretend even reduce it. As an example presence of dirt under dry conditions can be less harmful than in presence of oil since if no oil the particles can be eliminated but in presence of an oil film they can stay in the gap an work as a grinding paste. But let us speak about the cylinder, for same reasons as above many cylinders are designed to work with oil free air. The seals as well as the guide bushings are designed for it. The material they are made of has anti-friction properties and a very low wear as long as the manufacturer conditions are respected. For bushings the limit is the pv (Nm/s) which represent the product between pressure and sliding speed. The pressure is the consequence of side loading. If the pressures are too big and the velocity goes over a limit then the generated heat will reduce the material stiffness and wear can occur. Since side forces are the same on piston and rod bushing the wear will be more important at the level of the last since the contact area at the piston level is several times bigger and the speed is the same for both. More than that the area through which the generated heat can leave to ambiance is much more important for the piston-cylinder pair as for the rod-bushing pair.

When you react as you did you should first be more logical about the arguments you bring and know more about the stuff.

I very much appreciate your last suggestion it is very very professional.

Is it all air related or could the solenoid voltage be part of your problem? Not sure what your dealing with just asking.

This is a link to the valve datasheet:

http://www.norgren.com/document_resources/EN/5.4.148_7_99_Midi_Star.pdf

What's wrong with getting the local Sales Engineer from <...Norgren...> in for a discussion on the topic?