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Thread: Things You Should Know About 12 Volt Pumps

  1. #1
    Administrator Bob Williamson's Avatar
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    Things You Should Know About 12 Volt Pumps

    Some Things You May Not Know About 12 Volt Diaphragm Pumps

    12-volt diaphragm pumps are semi positive displacement pumps, unlike pressure washer pumps that are positive displacement. Semi positive displacement pumps are still self priming like their positive displacement cousins but the smallest inlet air leak can cause priming issues that can lead to cycling which can wreak havoc on your electrical system causing failure of the pressure switch and on high amp models the relay also, or simply a pump that will not prime at all leaving you scratching your head. Unlike leaks on the pressure side, inlet air leaks are not visible most of the time and harder to find. The more complex you make your inlet feed system with things like 3 way ball valves diverting to multiple tanks with bulkheads tapped into each tank your increasing your odds you will develop an inlet air leak, because not only do you have a 3 way ball valve for instance but you also have 3 threaded connections, 3 hoses slipped over the barbs and 3 clamps to come loose. Increasing your odds dramatically of having a problem. I’m not saying that you cannot use complex inlet feed systems but be aware of the potential pitfalls. We recommend using what we call the drop stick method. This is basically a 12' hose that comes off the inlet of the pump. At the pickup end of the hose you use a 45-degree elbow with a poly pipe threaded into the elbow with a check valve and filter at the end of the pipe. You simply drop it in the chemical tank to pull your mix and when you want to rinse the system or change chemicals you turn the pump off and pull the drop stick from the current container and insert it into your next container and turn the pump back on.

    12-volt pumps have a duty cycle. The duty cycle means the amount of time the pump motor can run before overheating. As the motor works it generates heat. Most manufactures recommend not exceeding an external case temperature of 180 degrees. We recommend not exceeding a case temperature of 140. The easiest way to measure this is by your hand. If you can hold your hand on the pump for 6 seconds or longer the motor is not to hot. If you cannot hold your hand on the motor for 6 seconds let it cool before operation continues. The addition of a cooling fan like we use in our Pump In The Box system will help extend the duty cycle of the motor. If you have a “Pump In The Box System” and your pump does overheat leave the on/off switch in the on position with the trigger gun in the off position. This will let the fan run without the motor running reducing the time the motor takes to cool. Improper wire connections, wire size, under rated switches, faulty batteries and excessive cycling can cause a motor to exceed its duty cycle faster.



    What is cycling? To understand cycling you first need to know how the pump works. A demand diaphragm pump uses a pressure switch and on higher amp draw pumps like the Fat Boy also use a relay to turn the pump on and off. The relay is used on higher amp draw pumps because the pressure switch is not capable of handling currents above 15 amps. So the pressure switch sends it’s 12 volt output to the relay to turn the pump on instead of directly to the motor. Cycling should be kept to a maximum of 10 cycles per minute. Typically a restriction in the outlet side of your system is to blame for cycling. It could be too small of a nozzle, a gun or ball valve that is partially open, a kinked hose or an obstruction in the system. When the pressure switch reaches 60 psi that is preset at the factory the micro switch contacts are opened to not let the positive current reach the relay or motor that then shuts the pump off. This system is designed to shut the pump off when the gun is closed. When you have a restriction in the outlet side of the pump the system builds up to pressure opening the switch turning the pump off and then as soon as pressure bleeds off it turns the pump back on causing a rapid on/off cycle. There are two reasons this is bad. First, the pressure switch and relay only have so many on/off life cycles and you use those quickly with rapid cycling. The second is called in rush current. When a motor first starts it pulls more current to get started then it levels out. This in rush current can cause heat build up in the relay contacts. This is why when you look at the rating on a relay it has two current rates one is in rush and the other is constant current. When your pump cycles off/on rapidly you will build up so much heat in the contacts of the relay they will weld together and your pump will not turn off. The Fat Boy pump comes from the factory with a 40/30-amp relay that is more than sufficient if the Fat Boy wiring is setup properly and cycling issue are avoided. The use of a larger relay would just be a band-aid for a cycling or wiring issue that could lead to a worse problem. Adjusting the pressure switch to shut off at a higher psi can also decrease the cycling issue. We do not recommend this because the higher psi draws more amps and the motor will exceed it duty cycle faster. In addition, even though the poly head on the pump is a good choice for resistance to chlorine it can harden the poly creating a situation that a higher psi can crack the pump head.

    Does hose size matter? When it comes to hose size there is a point of diminished return. Will a ¾” id hose flow more volume than a ½” hose in theory yes. But what you may not be taking into account is column pressure. Each foot of hose holds a certain amount of liquid as the hose diameter increases so does the weight of the liquid in the hose. This weight causes column pressure as the hose is elevated it causes backpressure on the pump, increasing psi causing the pump to work harder to push the heaver column of liquid. The same goes for the inlet also. The pump can only generate a certain amount of vacuum to self-prime. Manufactures of these pump recommend a maximum distance of hose on the inlet of 12’ with ½” hose. Increase the hose diameter and you increase the weight of the column decreasing the length that the pump can pull. Throw in a small air leak and the pump will never get primed. This theory does not apply if you are flood feeding the pump meaning you have the bulkhead fitting in the bottom of tank. When it comes to pumping chlorine solutions we all know that it is best to pull from the top of the tank to avoid leaks at the bulkhead.
    Bob Williamson
    Cleveland, OH

  2. #2

    Re: Things You Should Know About 12 Volt Pumps

    Thanks Bob that's good stuff to know. On my Fat Boy with the accumulator we have never had any cycling issues.
    Clark Hussey
    AP Surface Solutions LLC
    518-396-0972
    Non-pressure Roof Cleaning Albany NY
    Non-pressure House Washing Albany NY

  3. #3
    Great information! Thanks Bob

  4. #4
    Jr. Member hogwash_pw's Avatar
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    Quote Originally Posted by Bob Williamson View Post
    Some Things You May Not Know About 12 Volt Diaphragm Pumps

    12-volt diaphragm pumps are semi positive displacement pumps, unlike pressure washer pumps that are positive displacement. Semi positive displacement pumps are still self priming like their positive displacement cousins but the smallest inlet air leak can cause priming issues that can lead to cycling which can wreak havoc on your electrical system causing failure of the pressure switch and on high amp models the relay also, or simply a pump that will not prime at all leaving you scratching your head. Unlike leaks on the pressure side, inlet air leaks are not visible most of the time and harder to find. The more complex you make your inlet feed system with things like 3 way ball valves diverting to multiple tanks with bulkheads tapped into each tank your increasing your odds you will develop an inlet air leak, because not only do you have a 3 way ball valve for instance but you also have 3 threaded connections, 3 hoses slipped over the barbs and 3 clamps to come loose. Increasing your odds dramatically of having a problem. I’m not saying that you cannot use complex inlet feed systems but be aware of the potential pitfalls. We recommend using what we call the drop stick method. This is basically a 12' hose that comes off the inlet of the pump. At the pickup end of the hose you use a 45-degree elbow with a poly pipe threaded into the elbow with a check valve and filter at the end of the pipe. You simply drop it in the chemical tank to pull your mix and when you want to rinse the system or change chemicals you turn the pump off and pull the drop stick from the current container and insert it into your next container and turn the pump back on.

    12-volt pumps have a duty cycle. The duty cycle means the amount of time the pump motor can run before overheating. As the motor works it generates heat. Most manufactures recommend not exceeding an external case temperature of 180 degrees. We recommend not exceeding a case temperature of 140. The easiest way to measure this is by your hand. If you can hold your hand on the pump for 6 seconds or longer the motor is not to hot. If you cannot hold your hand on the motor for 6 seconds let it cool before operation continues. The addition of a cooling fan like we use in our Pump In The Box system will help extend the duty cycle of the motor. If you have a “Pump In The Box System” and your pump does overheat leave the on/off switch in the on position with the trigger gun in the off position. This will let the fan run without the motor running reducing the time the motor takes to cool. Improper wire connections, wire size, under rated switches, faulty batteries and excessive cycling can cause a motor to exceed its duty cycle faster.



    What is cycling? To understand cycling you first need to know how the pump works. A demand diaphragm pump uses a pressure switch and on higher amp draw pumps like the Fat Boy also use a relay to turn the pump on and off. The relay is used on higher amp draw pumps because the pressure switch is not capable of handling currents above 15 amps. So the pressure switch sends it’s 12 volt output to the relay to turn the pump on instead of directly to the motor. Cycling should be kept to a maximum of 10 cycles per minute. Typically a restriction in the outlet side of your system is to blame for cycling. It could be too small of a nozzle, a gun or ball valve that is partially open, a kinked hose or an obstruction in the system. When the pressure switch reaches 60 psi that is preset at the factory the micro switch contacts are opened to not let the positive current reach the relay or motor that then shuts the pump off. This system is designed to shut the pump off when the gun is closed. When you have a restriction in the outlet side of the pump the system builds up to pressure opening the switch turning the pump off and then as soon as pressure bleeds off it turns the pump back on causing a rapid on/off cycle. There are two reasons this is bad. First, the pressure switch and relay only have so many on/off life cycles and you use those quickly with rapid cycling. The second is called in rush current. When a motor first starts it pulls more current to get started then it levels out. This in rush current can cause heat build up in the relay contacts. This is why when you look at the rating on a relay it has two current rates one is in rush and the other is constant current. When your pump cycles off/on rapidly you will build up so much heat in the contacts of the relay they will weld together and your pump will not turn off. The Fat Boy pump comes from the factory with a 40/30-amp relay that is more than sufficient if the Fat Boy wiring is setup properly and cycling issue are avoided. The use of a larger relay would just be a band-aid for a cycling or wiring issue that could lead to a worse problem. Adjusting the pressure switch to shut off at a higher psi can also decrease the cycling issue. We do not recommend this because the higher psi draws more amps and the motor will exceed it duty cycle faster. In addition, even though the poly head on the pump is a good choice for resistance to chlorine it can harden the poly creating a situation that a higher psi can crack the pump head.

    Does hose size matter? When it comes to hose size there is a point of diminished return. Will a ¾” id hose flow more volume than a ½” hose in theory yes. But what you may not be taking into account is column pressure. Each foot of hose holds a certain amount of liquid as the hose diameter increases so does the weight of the liquid in the hose. This weight causes column pressure as the hose is elevated it causes backpressure on the pump, increasing psi causing the pump to work harder to push the heaver column of liquid. The same goes for the inlet also. The pump can only generate a certain amount of vacuum to self-prime. Manufactures of these pump recommend a maximum distance of hose on the inlet of 12’ with ½” hose. Increase the hose diameter and you increase the weight of the column decreasing the length that the pump can pull. Throw in a small air leak and the pump will never get primed. This theory does not apply if you are flood feeding the pump meaning you have the bulkhead fitting in the bottom of tank. When it comes to pumping chlorine solutions we all know that it is best to pull from the top of the tank to avoid leaks at the bulkhead.
    Good stuff, thank you.

    Mike Rhoades
    Hogwash Pressure Washing
    Lexington, North Carolina
    Mike Rhoades
    Hogwash Pressure Washing
    Lexington, North Carolina
    www.HogwashPressureWashing.com
    www.facebook.com/HogwashPressureWashing

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