Leak under bath sink

[woodman]

We own a 2013 Montana 3625RE. When I opened the driver side basement door, I noticed water dripping down from the water supply lines leading to the bathroom sink straight above the basement slam door. There are four PEX lines under the sink, a red, a blue and two whites. The water was coming from some type of water limiting switch that connected the two white lines. It was coming right out of the top of the device and not from the fittings. The red and blue were attached to the faucet and were fine. I was able to remove the device by unscrewing the compression nuts. I could not see anything that impeded it's operation, nothing was broken, but clearly it wasn't working. Fortunately, I found a local RV center that had one of these. They weren't aware of why this device was even used or why it was placed under the sink and neither do I. I installed the device, turned the water supply back on and everything is working fine. Anyone out there know the purpose of the pressure device or why it was located under the bath sink?