12 Volt Pump Support Page

Yes…we know, you are invested in a 12 volt system. Our condolances. So, in the spirit of community service, we present some support for you 12 volt pump victi…er...owners. We would never dream of putting a sales pitch in when you are suffering from 12 volt pump failure. So we won’t. 


Pump No Worky! 

Your 12 volt pump was never designed as a caustic chemical pump. It was designed to provide water for your shower in your remote cabin, spray weed killer, and wash down boats. Really. It was also designed as a CONSTANT FLOW pump, not to be restricted by smaller nozzles. Things tend to go bad when you try to get something to do a job it wasn’t designed for. And Murphy’s Law dictates that things are going to get FUBAR when you are 3/4 the way through that one big job you’ve been working on getting the past two years…that has a deadline. 

If you are in the middle of the Equipment Failure Kerfluffle…what do you do? You keep this page bookmarked is what you do. Then you call us after the stress is over and order you up an Outlaw pump. But we digress...


Solutions. Here are things you want to check. 


First, the Relay. 12 volt demand pumps work by sending a small voltage signal from a Pressure Switch on the pump to the Relay. The small voltage signal input from the pressure switch turns on the small switch which in turn triggers the big switch. The big switch allows high amperage 12 volt main power from the battery to flow to the 12 volt motor. The Relay is the little black box with all the electrical terminals coming off it, typically along with 4 wires…two big and two small. It clicks when the pump turns on and off. 

Relays fail...especially if you are short cycling the pump (see below). The EASY way to check for relay failure is by bypassing the low voltage relay switch. That is where the two small wires from the pressure switch go in. To bypass it, take a short piece of wire and use it to jump the two terminals between where the small wires come from the pump pressure switch. The relay *should* click and the pump motor should turn on. If it doesn’t, your relay is bad. Change it (you DO have a spare…right?) Get back to work. 

But what happens if you ran out of spare relays? Then wire the pump directly to the 12 volt leads and use the battery cut off safety switch (you DO have a battery safety cut off switch…RIGHT?!?) to turn the pump on and off. Have a crew member standing by to turn the switch on and off so you can finish the job. This assumes you don’t have backup relays and pumps on the truck…why don’t you have backup relays and pumps…seriously? It is a 12 volt pump we’re talking about! 

Of course the solution to glorious blissful cleaning lies Here

Under Pressure. 

Second, the Pressure Switch. IF the relay turns on when you do the above test, then your pressure switch is probably either misadjusted or it is kaput. Usually the latter. The pressure switch works by sensing the chamber fluid pressure inside the pump. When it drops below a set level, controlled by that little screw on the side, it opens a switch which sends a low voltage signal to the relay which in turn turns on a big switch that sends 12 volts from the battery to those big wires that hook up to the pump motor. The problem is, the pressure sensor inside the pump is often made from materials that are not terribly corrosion resistant. You probably run corrosive materials through your pump if you do exterior cleaning. Can you see where this is going? First, try adjusting the pressure setting on the switch…with that little tiny screw. Make note of where it is and turn it. The more you turn it in, the higher the pressure and the less flow your pump will deliver. Sometimes they get stuck. If the pump starts working again, count yourself lucky. 

If it doesn’t…and you already verified the relay works, then change the pressure switch. For this you will need to disconnect the pump. Make sure you drain the pump feed and spray line first…if you try doing this while the pump is hooked up and you have a few hundred feet of spray hose still up on the roof and the valve to your tank open, you will be shooting roof mix all over the place the minute you remove the pressure switch. Wear Chem gloves and eye protection anyways because…chemicals. You DO have chem gloves and eye protection on your truck…RIGHT? Now…if you DON’T have a spare pressure switch (or ten) on the truck, the solution to getting that job finished is to bypass the switch. You can wire in a small 12 volt switch (on the truck...in the spares...which SHOULD have had a spare pressure switch in them) between the pressure switch wires going to the relay. BUT…if you don’t have a small switch, wire the pump motor directly to the battery as above with a relay failure. Have an assistant standing at the truck by the small relay switch or the 12 volt battery safety cut off switch. That way they can manually turn the pump on and off. Do NOT run the pump for any period of time with no fluid going through it as in with the hose valve closed and the pump running…it will go boom. 

Motor Is Fried. 

If your pump motor is fried, it is done. Your pump is now a piece of scrap metal. The bearings on those pumps were never designed for constant operation at high heat. And when the bearings are gone, your pump is scrap metal. You can’t replace them like you can on the air diaphragm pum…um…right, no marketing.

Wiring…or how to avoid burning down your rig. 

It goes without saying that your wiring is going to be exposed to the elements. And corrosion happens. This is not only a reliability issue…it is a fire hazard. Back in the dark ages before we discovered the peace, joy and civilized tranquility of the Air Diaphragm Pump, we had a 12 volt system. A lot of them actually since they kept failing. And wiring was one cause of a fire onboard our rig. Why? Corrosion. When you have corrosion, you have resistance. Resistance=Heat. This is why an electric heater makes you warm and toasty. You don’t WANT warm and toasty when it comes to your pump wiring. Corrosion and resistance equals buring wire and a heavy duty $75 marine grade switch which resembled a marshmallow held into a campfire by a 2 year old. So, your wires need to be hefty (we switched to using 4/0 to the battery, and your connections need to be sealed within an inch of their lives. AND you MUST HAVE A BATTERY SAFETY CUT OFF SWITCH. Seriously. Of course we wouldn’t be so gauche as to tell you that Air Diaphragm Pumps have no wiring. Only tubes of refreshingly reliable air. Nah, we would’t dream of it. 


Soooo….you put your pump into a black battery Box. Aaannnd you turned your pressure switch all the way up, turning your "7 GPM pump" into a 2.5 GPM, voltage guzzling heat generating fire beast. AND you mounted that box on a black trailer…in August…in Texas. Your pump is now making making screeching noises. Yeah, it is borked.  

12 volt pumps generate a lot of heat. A Fatboy pulls 25 Amps running at 100 PSI. And 12 Volt pumps typically have ZERO thermal protection and barely minimum cooling from the fluid going through them. Overheat them and the bearings go belly up. There ain’t no repair kit for that. The heat needs to be dealt with. 

And while we are at it… Look, we have the greatest of respect for other resellers in the industry. But, we’ve got to call it like we see it. The pumps that are sold with the option that puts them into a closed battery box with a fan blowing on them…but no intake and exhaust to actually remove the heat makes no sense from a thermodynamic standpoint. It is like having a radiator fan for your engine then covering the whole radiator in plastic so no air can go through it. If you are going to put the pump into an enclosure, it needs to have both intake AND exhaust so the hot air can get out of it. A nice big 12 volt fan is the ticket…think big honking computer cooling fan. The intake should be down lower and the exhaust should be up higher…because heat rises.

Of COURSE we would NEVER be so crude as to mention the fact that Air Diaphragm pumps are self cooled due to the very nature of compressed air and literally cannot overheat. Seriously, it is impossible. We’d never do that. 


Battery. Get Charged Up.

Your pump is 12 volts and it needs a battery. So, you have a Deep Cycle Battery…RIGHT? Car batteries won't cut it. They are the absolute wrong thing to run a constant voltage draw pump as they are designed for high voltage transient draw with only a small amount of deep reserve. And for Gods sake, don’t wire your single truck starting battery in. After a day on the jobsite, asking a client for a jump start is just embarassing. Also, a battery might READ 12 volts (actually if it reads that low, it is DOA, should read above 13), but that doesn’t mean it will deliver that voltage during a load. Your pump might run if your battery is iffy, but it will run slowly and the extra strain will heat it up. Buy a GOOD deep cycle battery and a proper charger. 

Also, if your pump pressure is turned up, your voltage draw is exponentially higher and your battery needs to be bigger. 100 AH is a good starting spot. Gel Cell is best. Be prepaired, these things aren’t cheap. 

And for the sake of the battery gods...IF you are going to charge your deep cycle battery off your alternator, you MUST (repeat MUST) use an automatic charging relay (Blue Sea Systems) to prevent overcharging and sulphating the living cr@p out of that expensive Marine Deep Cycle battery you just bought. A Battery Bug is also a good idea to monitor the health of that costly box o’ acid. And have we mentioned before...your battery MUST have a safety cut off switch (see wiring, corrosion, FRIGGIN’ FIRE). Of course we won’t tell you there is no battery needed for our Outlaw Skid systems…unless you buy the Outlaw Ultimate skid with an electric start compressor and then you CAN use your car battery to start the compressor. Nah, we won’t mention that. 


We like to use humor, but this is NO JOKE. You can be hurt badly, so pay attention. Batteries are full of low PH Sulphuric Acid and they DO leak, both gasses and fluids. We use a lot of strong bases in exterior cleaning, Sodium Hypo and especially Sodium Hydroxide are extremely high PH Alkaline chemicals. Mix A strong Base and a strong Acid together and you get instant toxic gasses (as in WW-1 trench warfare death gasses) and you are as likely as not to have yourself an explosion. KEEP YOUR BATTERY AWAY FROM YOUR PUMP AND YOUR MIX TANK…IN AN ENCLOSED BATTERY BOX. 

It also goes without saying that if you keep acids on your truck for doing concrete or wood that they should be stored as far away from Sodium Hypo or Hydroxide as physically possible and you need to do everything possible to EVER avoid mixing them. Besides the Toxic Death Gas that is generated…so rapidly you will NOT believe it…it can blow up causing severe injuries. Never mix Acid and S.H. or Hydroxide solutions in the same container EVER. We want you guys to be safe. 

Preventing Short Cycling…or How to Quickly Kill a 12 Volt Pump. 

If you understand how a 12 volt pump works, you will understand how short cycling can quickly kill its' ability to pay your mortgage. What is short cycling? To explain, we will have to explain how 12 volt demand pumps work. 

A 12 volt demand pump is a constant pressure pump. In other words, it tries to deliver fluid at a constant set pressure and flow. It does so by the use of a pressure switch. When the pressure switch detects a drop in the pressure of the fluid chamber as fluid is released from the output from the pump into the spray hose, the switch opens and sends a signal to the relay which opens the 12 volt connection from the battery and turns the pump motor on. The Pressure switch is always trying to maintain the set pressure it is adjusted to. Close the spray hose valve and the pressure in the fluid chamber builds back up and the pressure switch contact closes and turns off the pump. This is why there is a small delay between when you turn the spray valve off and the pump turns off. 

Here in lies a major weak point with 12 volt pumps. Say you are on a roof and you have a section you need to spray right next to a bunch of wood trim. You don’t want to get mix onto the trim and your big 040 nozzle running wide open isn’t going to do it. So,  you either slap in a smaller 010 nozzle or you turn the ball valve way down to restrict the flow to prevent from having to refinish the siding. What happens to the pump? Back on the ground, the pressure switch sees a drop in pressure and it turns on. But since the flow is now resticted and thus very low, the pump chamber pressure builds back up very rapidly…and the pressure switch turns off. Then it drops again as fluid trickles out at the other end and the switch turns back on. Then Off. On. Off. Rapidly. The pump will literally rapidly cycle on and off.

This is known as Short Cycling and it is probably the most effective way to kill a 12 volt pump. Well, most of the time it will kill your relay as it turns on and off rapidly…literally welding itself from voltage spikes. But, it can also kill the pump by rapidly spiking the turn on voltage and heating the motor up. Without any flow of cool liquid to at least give it some sort of chance, bye bye pump. This is why Electric Pumps have a very limited range of flows, especially on how little flow they can deliver, That number is typically one step down from the pump output. So, if you have a “7 GPM” pump (which is really 4 GPM derated) you should normally run a 4 GPM…or 040 nozzle. This is what the Fatboy 4 banger roof cleaning nozzle sets are. You *can* go down to a 3 GPM, or 030 nozzle for a limited period of time. 2 GPM you are in the danger zone. 

Now would be the time for us to point out that it is literally impossible to short cycle an Air Diaphragm Pump. Doesn’t matter if you want to throw an ultra fine mist nozzle on it, an AODD pump simply doesn’t care.

Accumulator Tanks. What Do They Do?

A lot of 12 volt sysems are sold with an Accumulator Tank as an option. So what is an accumulator tank and what exactly does it do? Well, if you read the above section on short cycling, an accumulator tank is an attempt at mitigating that problem. The accumulator tank is simply a small container that holds a small amount of fluid stored under pressure. It is actually nothing more than a passive AIR DIAPHRAGM PUMP! Funny how to solve a problem with an electric pump, they turn to an air diaphragm pump! What the Accumulator tank does is to accumulate a small amount of fluid under pressure in the chamber behind a diaphragm. If you look at one, you’ll notice it has an air inlet and a fluid inlet and outlet. You pump air into that inlet and as the pump fills up the chamber, the diaphragm pushes against the fluid, pressurizing it. This added fluid is designed to act as a buffer, a pressurized fluid reserve the nozzle can draw from when there is a small amout of fluid running through the system. It also helps with a pressurized source to help start the flow when you have a large amount of lift. It is designed to delay…not prevent…short cycling. It allows you to more safely run an 030 nozzle instead of an 040 nozzle on a Fatboy or the like pump. 

The PROBLEM with an accumulator tank is that it has a limited time it will work since there isn’t much fluid in it. AND nobody makes a chemically compatible one. That is because they are all designed for WATER. They are either big and metal…which rusts, or you use what nearly everybody does...a Flojet 30573. The FloJet is the one everybody buys. It is a single molded unit made from Polypropylene with a diaphragm that is non replaceable. And…that diaphragm is Buna-N. Which is Rubber. Which is made stiff and then destroyed by Chlorine. Yeah. Plan on replaing them about every 6 months in a busy cleaning operation. 

An Air Diaphragm Pump doesn’t need…well you know. 

The TRUTH About Pump Flow Ratings. 

We see people constantly posting about their “7 GPM” electric pumps. Are they actually 7 Gallons Per Minute? Well…yes and No. Unfortunately most people do not understand pump flow specifications. What the sales pitch does not tell you is that the 7 GPM pump you purchased will NOT do 7 GPM…at least not at the pressure you run it at. All Pumps are de-rated at pressure. Remember, Electric demand pumps are constant pressure pumps and in order for your to hit a roof from the gutter line through 200 feet of 1/2” hose, you need a certain amount of pressure to overcome the pressure the hose and the column of liquid going up the ladder adds to the pump head. Most 12V pumps come set for 60 PSI and many guys turn the pumps up to 100 PSI in an attempt to get that last few feet. What does this do to the flow? It does what any pump does when faced with higher pressures…it reduces the amount of output. Your 7 GPM pump is actually 3.8 GPM through 200 ft of 1/2” yellow hose at 60 PSI…on the ground. It is about 2 GPM if you have the pressure set to 100 PSI. And those who buy the 5.5 GPM 5250? They set them at 100 PSI. 1.9 GPM. Yup.

Remember, there are losses when you have the fluid going through hose (which is why we recommend 5/8” hose for 1/2” pumps). This is why we start with higher flow pumps on the systems we build. So by the time the pump is derated at pressure, it can still deliver enough flow to work when you need it. Air Diaphragm Pumps can deliver VASTLY greater amount of flow. We’ve got some that will do FIFTY GPM and one in the shop that will do 180 GPM. No bull.  

Don’t Believe Us on the flow numbers? Here is an output flow chart for a Fatboy Pump. Trust us, it is not easy to find. This is no different for any of the 7 GPM rated 12V pumps. This is at the pump head BEFORE you have any flow or pressure losses from your spray hose. 

Because Physics. 

So…buy an Outlaw Pump System and be Happy! See. We controlled ourselves and got in that one little piece of marketing at the very end.