It’s been a while! Between lots of work, travel, holidays, RV projects, etc., I haven’t written anything here in a while. But this time I’m writing about something I wish I’d done a long time ago, before I was also fighting a water leak: getting rid of the noisy, pipe-rattling water pump that slows to a trickle if you try to run more than one thing at once, in favor of a more powerful jet pump.
In the past, I’ve talked about ways to make the regular RV pump work better, but a second diaphragm leak in as many years had me frustrated and looking for a better solution. I decided to roll the dice on a different approach–a jet pump meant for shallow well applications.
What’s different about a jet pump?
So first, let’s talk about the typical RV water pump. It’s a positive-displacement, self-priming pump. What that means is that for every revolution of the pump’s motor, same amount of volume is supplied to the RV’s plumbing system, largely independent of pressure. It’s basically a 3- or 4-piston/diaphragm single stage arrangement–the diaphragm opens, filling with water from the tank, then expels that water into the water system. Being self-priming means that it generates suction when there’s no water in the pump housing itself. In almost all RV applications (short of park models), they run on 12V DC power, drawing about 4 amps (~40-48W) running. They usually cycle on and off with a pressure switch mounted to the top of the pump housing. While they still cost about $100, the pump itself is all plastic.
A jet pump on the other hand combines a centrifugal pump with a venturi/jet arrangement. A centrifugal pump can be found in all kinds of applications, from the water pump on your car to the 9,000 hp pumps circulating water through a pressurized water nuclear reactor. The centrifugal pump ejects water through an orifice that creates a venturi and draws more water in. It’s continuous operation, as opposed to the discrete intake and exhaust cycles of each diaphragm in a normal RV pump, means it won’t rattle pipes and the water delivered to your fixtures won’t have the same pulsating effect you might be used to.
Pump Selection Criteria
Here’s what I was looking for:
- Reasonably compact size. I knew it was going to be bigger than the outgoing pump, but I didn’t want to lose more space than I had to.
- Capability to deliver reasonable flow at reasonably high pressures. Beating the old pump at a minimum, hopefully able to sustain enough flow in the shower while the washer tub fills.
- Good for potable water.
- Quiet(er). Low bar relative to the old pump.
Let’s get the not-so-good out of the way first. A jet pump isn’t going to be self-priming. In other words, if we just hooked it up and turned it on, it would run without ever moving any water. It also doesn’t come with a pressure switch, so we’ll have to add one in separately (as it turns out, this will end up being an advantage).
The particular jet pump I purchased is about the smallest I could find at 1/2-hp, with a stainless-steel impeller. It’s rated at 960GPH peak flow–that’s 16 gallons per minute–and has no trouble with 55 psi.
Products from Amazon.com
Price: $23.29Was: $27.10
What else is needed?
I already mentioned that the pump doesn’t integrate a pressure switch. This is easy enough to remedy, either off the shelf at the local home improvement store or from Amazon.
Given that the pump is rated for 55 psi, I went with a 40/60 pressure switch. But not just any pressure switch–this one has a lever on the side. In addition to cycling on and off between 40 and 60 psi, as pressure falls, it will also open to prevent the pump running non-stop dry. For a rig with washing machine and dishwasher, this provides some peace of mind that I won’t ruin the pump if I run out of water while not there to catch it.
. It’s pretty cheap, and does the job well. If you don’t have pressure in the system (say, first time or after you’ve run the tank dry) you have to momentarily hold the switch arm to start the pump. After that, it takes over, and works unattended until you run out of water.
Unlike the outgoing RV pump, a jet pump like this doesn’t internally prevent flow backwards to the tank when the pump stops. While the pump installation instructions called for two check valves, the minimal vertical distances between tank, pump and water system really don’t warrant it. The check valve I used can be picked up at Lowe’s/Home Depot or Amazon for about $10.
Since we have two purposes, but only one valve, we need to locate it so it does both. We want to prevent flow backwards through the pump, but we also don’t want to lose prime when the tank runs empty. That means the valve needs to go on the supply to pump, not between the tank and the water system.
At the very least, you’ll need to run a line between check valve and pump. You’ll also need to adapt the typical 1/2″ plumbing in the RV already to the 3/4″ inlet and outlet on the check valve, and the 1″ inlet and outlet on the pump. A few lengths of PEX tubing and crimp rings, fittings, etc., will be needed depending on the space you’re working in.
Ok, so you tried it. How well does it work?
Awesome! Compared to what I suffered with before, it’s a huge improvement. It took more than I expected (about 24oz.) of water to prime, but I’ve only done it once.
Going from no pressure to 50 psi only takes a few seconds. That includes building pressure against the 2-gallon accumulator in the system. (You do have an accumulator, right?) Yet it isn’t so quick that the pump cycles on and off while doing stuff.
I can also turn on more than one fixture at a time, without flow slowing to a trickle. Someone flushing a toilet, or the dishwasher or washing machine filling no longer puts a shower on pause. The pump definitely makes noise, but it’s an easily muffled noise–much higher in frequency than the old pump. Maybe something along the lines of a blender, without anything in it.
I’ve also run the tanks empty a few times. The pressure switch cuts power to the pump just as it should, and the pump doesn’t need re-primed afterwards. Like the old pump, you can tell when you’re starting to hit the bottom of the tank. It’s a different behavior though. I’d normally notice the pipe-rattling frequency change with the old pump, now it starts ingesting air and spitting. You know you’re about to be out of water, with enough time to do something about it.