Teach me about water pumps?

[Jamespio]

Okay, I'm totally new to RVs, and I've taken on a complete rebuild of a 69 overlander. I'm a number of steps away from getting serious about plumbing, but I had some questions.

First, I found, uninstalled, the original water pump. At least I assume it's original. Has a little toothed belt on it. Were these any good? Do I want to use it (assuming it works), or is it a museum piece that should be replaced now rather than having it conk out in the middle of a camping trip?

Next, just a general question: how does a water pump know when to work. I understnad how pumps work, my question is simply what tells the pump to begin pumping? Is the water system always under pressure? Or does opening a tap somehow tell the pump to start pumping?

[Jamespio]

Here's a pic of the pump I found in the trailer:


Also, attached to it is this thing:


What is it?

Final water pump question. How is it wired? Is it just two conductors?

[Silverflames]

The pics did not post.


Most new 12 vlt pumps have a built in pressure shut off switch. When pressure drops to a set amount it turns on, when it rises to x amount it turns off. Not sure about your set up, but I use a relay and the switch on my control panel to power on and off. Some older units had a air pump that would pressurize the fresh water holding tank. Me I would belly up the money and put a new one in. Less worry and hassle,

[TG Twinkie]

The pump you have is a PAR pump. They were a good pump and some can be rebuilt.
There is usually a pressure switch wired to the pump that has preset
ON and OFF limits. When the pressure drops below the lower preset level the pump will start. When the preset pressure rises to the upper preset level the pump will stop.
If the wires on the pump are RED and BLACK, Red is positive and Black is negative.