Chiller flow switch troubleshooting

[reftec021702]

Dear fellows:

I am working on a YORK 100-ton chiller which fails to start every morning. According to the operator, the display indicates a no flow condition, even with the chilled water pumps running. Sometimes a little bump to the flow switch casing is what is needed to get the chiller running. A previous engineer hinted a piping system air lock situation.
I have been exploring this suggestion and have found air vents located throughout the system. Also, the fact that just some hitting to the flow switch engages it, makes unlikely the air lock scenario, I think (this bumps will not get rid of air in the pipe). Any other explanation?

 

[krb]

What type of switch is it? Paddle switches are generally unreliable, and can give false readings.

 

[simsd]

Okay,

A couple of things to check for.

1. Depending on the type of flow switch, try taking the cover off and see if it makes with the pump running.

2. If not, then take it out and see if the paddle has the ability to stroke freely.

3. See if the paddle can run a fully stroke in the pipe. Generally the arm that holds the paddle needs to be in the pipe as well as the paddle.

 

[UDP10]

We've quit using paddle switches for chiller flow verification. We've retrofitted most of our chillers to DP. It's not an expensive change and its much more reliable.

 

[lilliput1]

Switch contacts eventually get worn off because of arcing. Replace the unit. DP switch is better but you need to make a another tap in the line to sense DP across the chiller. You need one in the chilled water line & another in the condenser water line. They are needed to protect the chiller, preventing it from running if there is no condenser water or chilled water flow.

 

[simsd]

True