[Ehsan]

i have been facing a problem since a long ago. I got 3 way motorized valves(honeywell) installed at AHUs to by pass the flow with the set point (through thermostat).These valves keeps on stucking and i have tried many things like lubrication of spindle, checked the motor power etc but i am unable to find the fault why does it stuck again and again.
i may be missing any other thing that u ppl may know about it.
i need the possible reason that why these valve stucks continuously.note that these valves are installed in a closed hydronic system in central AC plant.
thanks and regards,

 

[ckartson]

Are they piped properly. What model are they. Some valves will do that if they are mixing valves but piped as diverting. Also could the press diff be to high. Might want to check your valve specs.

 

[timebuilder]

Is this in a commercial application?

 

[Ehsan]

ckartson thank you very much for your reply i will provide you the specs early. the valve is installed to divert the incoming flow or to bypass the flow (chilled/hot water flow when set point is achieved) These valve have been working for years but suddenly these valves are producing this same type of problem. Can you please enlist the general reasons that why does motorized valve stucks??

high pressure difference may be the reason i will check this out if this is the reason.
i need probable reasons why do these valve stucks..

 

[Ehsan]

ckartson thank you very much for your reply i will provide you the specs early. the valve is installed to divert the incoming flow or to bypass the flow (chilled/hot water flow when set point is achieved) These valve have been working for years but suddenly these valves are producing this same type of problem. Can you please enlist the general reasons that why does motorized valve stucks??

high pressure difference may be the reason i will check this out if this is the reason.
i need probable reasons why do these valve stucks..

 

[Ehsan]

This is in the AC plant for comfort cooling/heating.
It is being used in Air Handling Unit for diverting the chilled/hot water flow when the temperature reaches to its set point.

 

[Ehsan]

one thing more this is in the close loop (chilled/hot water loop) and due to the stucking problem motor for driving the valve gets damaged continuously.

 

[ckartson]

There are two types of three way valves. Mixing and diverting. Mixing has two inlets and one outlet. Diverting has two outlets and one inlet. If piped wrong (mixing as diverting or vice versa) valves can get stuck. You may want to google mixing vs diverting for piping examples. Water quality may also be an issue. Rust in the water or black particles may require additional filtration (sidearm filters) to clean it up.

 

[catmanacman]

Could have crap in the system

 

[Ehsan]

i know the difference between mixing and diverting valve. In my application this is mixing valve. But the problem rises again and again.How does greater pressure difference stucks the valve?? you mentioned that pressure difference can be an issue. Would you plz tell me how it can become a factor for valve stucking condition. or any other reason for that why 3 way valve stucks again and again???? your reply will be highly appreciated.

 

[timebuilder]

I doubt if you've had a change in system pressure that caused this behavior to begin.

It is far more likely you have a particulate or water chemistry issue which is causing the valves to stick.

 

[ckartson]

Ok so you have confirmed that they are mixing valves so two things are left. Water chemistry and dif pressure across valve. As stated by Time builder your system characteristics should not have changed. If the flow across the valves is to great it's possible that the flow itself can overcome the spring in the valve and hold the valve in one position. Checking pressure drop across the valve if petes plugs are installed would be one way to test. Checking system pressure diff at pump would e another. You haven't replied with what model valves or actuators you have so my mental picture is the Honeywell zone valves with the spring in the cartridge (don't know the series off hand). Third and most likely is very dirty water. Filtering and water treatment would be the solution.

 

[Ehsan]

thanks buddies for your experience sharing. i have tried to find the model no for the valve but i am unable to find any. these valves are installed since a long ago the name plate is not in a condition to give information. there is no place to check the pressure difference across the valve but this valve is installed to bypass the chilled water from cooling coil. I have checked the pressure difference across the coil its 5~6 psi. water quality is fine enough as this is being regularly monitored.it is installed on 4 inch pipe. i am trying to get the model no but uptill now i am unable to find it..

ckartson if i am not wrong i got your point this way " i the flow of water is greater it may hold the valve in one position and do not let it move freely untill the motor power is greater enough to overcome this holding effect of flow" i am i right?

 

[Ehsan]

is there any one? okartson????

 

[HVAC_Marc]

put up a picture of the valve

 

[Ehsan]

Give me the ans i asked dear

 

[gbfromsd]

Valve shaft where it passes through the seal can in time accumulate deposits that cause it to bind as the stem moves. The electrical actuator can only generate so much force and in some cases the differential pressure across the valve may make it work even harder. Also, some of the older style actuators are really just small DC motors that weaken over time. Things wear out. Cant be sure that this is an issue without seeing it.
Still, I'm a bit confused when you mention pump damage - whether it's bypassing or flowing through the coil the pump should see the same gpm if your piping is setup like most. Might be worth looking at the piping layout to see if your deadheading when bypassing. Also, the valve itself might have a valve stem that allows the actuator to be mounted in more than one position - only 1 of which is correct.

 

[Ehsan]

thanks gbformsd for your kind comments.Actually this 3 way valve is installed at Air handling unit. The chilled water comes through a pipe to coils of AHU but before entering the coil there is a link taken out of this inlet line which is connected to the chilled out line (the outlet line from coils of AHU) for bypass purpose when temperature meets the settings. The valve is horizontally positioned in a way that if valve is 100% close it restricts the bypass flow and allows the chilled water to completely pass through the coils and if it is 100% open, all the flow is bypassed and no flow passes through the coils. It can be in between position where some of the flow is bypassed and some of the flow is passed through the coil. This valves positioned itself by sensing the temperature of air being chilled.