SylvanLMP
quote:
Originally posted by [email protected]:
Sorry, but it has been impossible for me to reply to your answers. I¡¦m up to my eyes at the moment.
I work in Spain and we¡¦re trying to redesign a thermostatic valve, because we want to sell it in England. But our valve doesn¡¦t work as well as we expected because of this ¡§valve chattering¡¨. I didn¡¦t know what this meant and what causes it.
The valve is pneumatic controlled, with no electronics. It begins chattering in a working point, as I told before, when is near to be closed. At this point, the water flow is 50 l/s. The valve must work correctly by itself. So, a globe valve before our valve is not the right way.
Our problem is to guess the reason of this valve chattering. We have three possibilities:
„h If the chattering is due to high velocity through the valve, the pressure can fall down the saturation pressure. This could be cavitation.
„h Some kind of vibration can cause resonance with the spring.
„h Finally, water hammer is our last option. But this is often caused when you close a valve quickly and you have a large mass of water.
Weave measured the noise. It¡¦s too noisy to be cavitation. With the frequency we¡¦ll be able to say if it¡¦s some kind of resonance or water hammer.
What do you think about this? Could you think of any new reason for the chattering?
Thank you very much. Happy New Year.
Thank you sir for CONFIRMING my Assumption it was PNEUMATICS.
“The valve is pneumatic controlled, with no electronics”
The problem associated with this type of modulating action is as follows.
Electric valves are either NO or NC
Electronic and Or Pneumatic are modulating and thus can cause a “hunting effect” chattering.
What you can try is reversing the valves action as follows Have this valve in the normally OPEN position and using the “controller” to close the valve when the desired SET POINT is reached.
The beauty of having a Normally Open valve is in this fail safe mode you will have constant circulation thus less chance of freeze up.
As a chief Stationary engineer I used to Calibrate these types of valves and if you adjust the air pressure you can eliminate the hunting.
Double check your set point to the actual travel distance on the actuating piston or diaphragm.
You may also want to increase SLIGHTLY your orifice to over come the possibility of excessive velocity especially during valve opening or closing.
What I did when installing steam stations (high pressure 125#+) was to use several step down valves prior to using the steam to heat domestic hot water and absorption systems for my Air conditioning Environmental Controls.
If your having problem controlling various valves do to different application / pressure /volume needs try adding slightly more resistance to the piston assembly VIA higher tension springs etc.
Unfortunately after I turned 27 I no longer found heating that interesting and thus gave away all my heating testing equipment BUT what you could try is set up a test bench like I did when repairing these devices and put a Gauge on either side of these valves and test for the following.
Charge the system and then modulate the valves like under system demand and see when the chattering starts WHAT pressure then you can try a slower closing valve design like we used in the Navy on flushometers a Naval flushometer like a Sloan type that uses hydraulics.
Too bad your so far away as It would be fun working this kind of problem out.
I had something like this going on in Rhoda Spain at a Winery BUT those were the days I worked cheap and didn’t mind traveling 
This winery was trying to maintain an exact temperature for the wine.
Ah those Benefits working in the big vats .
I am sure your problem can be repaired by simply hit and miss with the valves opening sizePLEASE feel free to Private E mail me again. Sylvan
