pneumatic thermostats

grindog

we just started doing service in an old building that has a two pipe steam system. One of the tenants has a radiator that wont stop knocking, there is a pneumatic solenoid on each side of the radiator. the radiator is getting hot when the system is on so i am thinking that the solenoid on the condensate return is not opening.
I have no experience with pneumatic tstats or these type of solenoid valves. Can any one here give some suggestion on what i should look for to trouble shoot this problem?
There are no steam traps any where to be found and only some of the radiators are set up like this one. I am thinking about taking out the pneumatics and installing a danfoss two pipe trv and if this works the tenants will have them installed on all radiators and demo the pneumatic system. Any suggestions ?

Mike T., Swampeast MO

Pneumatic control systems are generally used for their inherent proportional control ability. I certainly don't claim to know much about steam systems but I'd say there's a good chance you're not looking at "solenoids" in the typical sense.

Blackoakbob

Soleniods in a sense.....

that they open and close, but what I think you have is a pnuematic zone valve. These valves look like they could be a solenoid but really open proportionally with the air passing thru the stat. A simple check out is to pull the stat out of the base in the wall and allow the air to bleed freely. This will vent all the air from the control line to the valve and cause it to open fully. You could pull or disconnect the line from each valve, but this way will answer two questions: is there air to the stat? and are the valves opening and closing? From this point you will need an accurate gauge, 0-30psi, or a pnuematic thermostat calibration kit available from Johnstone Supply or Grainger, Inc. I'm not sure why you would have to valves on one baseboard, but from what I hve seen and what I have read here ANYTHING is possible. I hope this helps. Best Regards,

jim lockard

Take

the Air line off of the valve see if it changes state (opens or closes ) do you have air coming out of the hose? Do you have a T-Stat Needle and a gauge? read the stat. Been a while since I have done air find your set point on the stat above or below the set point you should change state. May want to check the valves Rubber bladder if that has failed nothing will happen when air is applied.

Al K._2

Pneumatics

I'm thinking something other than the pneumatic controls is causing the knocking. Not to doubt, but are you sure there's control valves on both sides of this rad? Not all radiators having control valves may be part of a long-lost zoning strategy. Adding thermostatic valves may be a nice addition to the system to provide individual comfort. If you can provide some more specific info on this system, such as control mfg., I may be able to provide more info as to check-out of the thermostats and control valves.
Thanks,
Al K.

clammy

maybe

I have seen this set up on coils in older building i believe there operation is as so when the condensate trap senses condensate as the traps open it vents the t/sta air line which starts to close the supply valve as the trap closes upon sensing steam the the air vent on the trap ( from the t/sta or supply control valve )will stop venting and the suppl valve will start to open .I believe they used this set up to pervent a rush of incoming steam to the coil as the pressure dropped from the trap opening .I would go over the pneumatic supply valve and check the by pass on thetrap to ensure when the trap opens that it by passes acontrol air out modulating the supply valve closed .As others have stated check air presure ,diapharms ,t/stat calbration and set point pressures ,linkages for the control valve and the return piping for obstructions good luck and peace clammy

Gene_3

why

is there a pneumatic valve on the in& out of the radiator???????? there should be a pneumatic on the in and a condensate trap on the out, it sounds like you do have water trapped and when it hits the steam,bang.

If you do have a trap that may be your problem not the pneumatics.

Pneumatics is a course in and of itself, DO NOT TRY TO ADJUST THE T-STAT OR ANYTHING IF YOU'RE NOT SURE. no good will come of it, you need the test kit for the brand you have, the tstat may have a DA or RA on it, Direct Acting-- Reverse Acting, which means rise in temp-rise in pressure DA, rise in temp-drop in pres RA, just for openers

the valves have a diaphram , that may be leaking, you may hear it, but the kit is usually required to test--
!!!the spring is loaded!!! DO NOT TAKE IT APART WITHOUT READING THE INSTRUCTIONS you do not want to spend the rest of your life answering this question {WHAT HAPPENED TO YOUR FACE?}

you need to get a pro well versed in your system and it's components, from the components you describe you need help

grindog

we found more out today

thanks for the help, there are valves on each side of the radiator.supply is 1" and the return is 3/4" they are johnson valves that are spring loaded and the bladders are in good condition. The stats are robert shaw.
This building is over one hundred years old and there are about ten condos total. We were able to finally get into one of the basement units this morning to lookat at more work and saw that all the hangers that supported the condensate main were taken out. It was back pitched and full of hot water.
I will try to test the air lines for preasure next time we go back but what i think is happening is the condensate main in the basement is not hung and pitching backwards the condensate is backing up the riser and causing the problem. The boiler is on a timer and runs a long cycle in the middle of the nite waking the tenant. that is the only time that the radiator starts to bang. We have found no steam traps any where they all dump into a drip leg that goes into a condensate receiver pump. They ordered us to fix the condensate piping so i hope that fixes everything. Will keep ya posted.

will smith_4

If you have two pipe steam, there HAS to be a trap. On a pneumatic system, on a call for heat, the stat will drop pressure to the valve at the convector, and the valve will open fully. As the temp rises, the stat will send pressure to the valve, and throttle it off. Anything is possible, but I have never seen a pneumatic valve installed on the return