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Old 03-01-2012, 09:44 PM   #1
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Trap primer curiousity question

I've noticed something I can't figure out about the plumbing in the restrooms at work. The lavs in these restooms have some type of electronic faucet; there's a sensor near the lav and apparently a solenoid operated valve in the adjacent mechanical room (no valve is visible underneath the lav). There are two such lavs in most of the restrooms; a few have four. Each restrooms also has a floor drain.

In every restroom that I've checked so far, there is a trap primer for the floor drain that is tied into the rightmost lav. After that lav is used, about 15 seconds later, you can hear water run into the floor drain for a few seconds. Straightforward so far. However, the lav itself also has a trap primer, which runs for a few seconds after the floor drain trap primer. Only the rightmost lav has this trap primer. Why would a lav, especially one in a large office building's restroom that is used frequently, need a trap primer? And why is only one lav in each restroom so equipped?


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Old 03-01-2012, 10:06 PM   #2
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What type of trap primers are they?

The ones we use are operated off of pressure drop in the entire system. Using one fixture exclusively to set off the primer would not really be an acceptable means of priming the trap.

The way you are describing it really makes no sense. The solenoid for sensor faucets that i've seen are usually internal, but depends on the make. Some are very different. I'm not even sure what the solenoid has to do with the trap primers anyway.

Are you sure that there's a trap primer on the lav trap? Maybe it's a condensate inlet or something? Can you actually see the trap primer devices?

This post is so confusing.


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Old 03-01-2012, 10:08 PM   #3
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I have hooked HVAC drains to lav tailpieces. Could that be what you saw?
I did plumb a residence hall at a college once. All showers and lavs had primers because the building was empty during the summer
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