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atikovi · 10-08-2011, 12:54 PM

I replaced the 30+ year old pump in my '79 Santana camper van with this Shurflo pump.

This camper only has a sink that uses any water so this pump was overkill but I thought it will last forever if the original pump lasted this long. The faucet has an electric on off switch controlling the pump and when you turn it on, water comes out the faucet with so much force it splashes all over the counter. Can I drop the voltage to the pump to slow it down? I tried two 1 ohm 10 watt resitors in series between the fuse and switch and it was just about perfect. Will this damage the pump motor? It only runs a few seconds at a time. The resitors get hot, will it cause a fire?

LVJ58 · 10-08-2011, 01:15 PM

You might check to see if you can install some type of pressure regulator on the output side of your pump. Don't think I would mess with lowering voltage as it may damage the motor, but not sure.

Good luck....

Ramblin · 10-08-2011, 01:15 PM

Can you replace the faucet with a standard one? The pump is designed to maintain pressure. It will come up to pressure, then shut itself off. If you had a standard faucet, you could leave the switch on and regulate the flow with the faucet's knobs, as you would at any sink.

mr300ce · 10-08-2011, 01:22 PM

Good/new faucet really made my kitchen sink a wonderful thing of beauty. A new swivel end piece was a marvelous improvement.

The aerator screen really helps control the splash you are talking about.

The resistors you describe lower the voltage to the pump, and really should not harm the pump. Route the resistors so they are not touching anything and you should be OK.

atikovi · 10-08-2011, 01:37 PM

I already put in a new faucet of the original design so I don't want to change that plus there is no room for a restrictor. Added the resistors to the curcuit and have just the right flow.

Have the resistors near the pump taped together. I'll put some aluminum between them and the carpet.

EngineerMike · 10-08-2011, 01:41 PM

IIWMI'd put a restrictor in line or replace the faucet. Running a motor at too low voltage would ruin an AC motor, not sure about DC but not worth the pain. The Revolution pump you are now using should be a good one for as long as you care about the camper. Fixing the faucet would be best IMO. If you want to do the restrictor, you'll need a fitting inline on the output side; start w/a teeny hole in a blank washer (might find a suitable brass washer- ACE hardware, etc.) and drill it out till flow works for you. But I think you'll like the new faucet better.

ottffss · 10-08-2011, 02:45 PM

Let's see, the pump draws 7.5a at 12v = 90watts.
The resistors added are 2 @ 10ohm 10w resistors in series = 20ohms at 10watts

90watt draw thru 10watt capacity resistors

Yep, the resistors are going to get very, very hot.
Yep, in time the resistor will burn itself out.
The question is will the resistor(s) burn out (open the circuit) before (or after) it reaches a combustible temperature? (BTW you are playing with fire here, foil or not)

Other options.....
Get higher wattage resistors (which will still get hot) remember resistance=heat
Add a small tube "bypass" that runs back to the tank off loading some pressure
Insert a constrictor someplace on the output side of the pump (never the suction side)

wa8yxm · 10-09-2011, 01:46 PM

Modern RV water pumps have a pressure cut off, but they are designed to provide water for a shower or a flush, not just a sink. Normally the sink has a valve that restricts the flow of water.

Cut into the line and put a valve in the line, adjust the valve so the water flow is... More within your liking. (That is the water line) don't drop voltage, that will cause other problems, restrict the flow of water OUT of the pump.

TQ60 · 10-13-2011, 12:55 PM

OK, 7.5 amps on 12 Volts is 90 watts. (P=I*E)

12 volts divided by 7.5 amps indicate the resistance of the motor is 1.6 ohms (R=E/I)

Check
1.6 Ohms * 7.5 amps is 12 volts (E=I*R)

If we add 20 ohms of resistance in series with the motor, the new total load resistance is 21.6 ohms.

So with I=E/R, 12 volts/21.6 ohms= 0.5555 amps

So 0.5555 amps * 12 Volts = 6.666 watts

So 10 Watt resistors will get hot, but as long as they are mounted where they can properly dissipate the heat they will last a good long time.

BUT the motor was designed to operate at speed, and to do so requires it to have full voltage.

Granted the 7.5 amps is fully loaded at the rated pressure, and operating into an open orriface would be little load on the motor.

So as long as the pump is running for short intermittent duty cycles it should not get too warm as the resistors being the highest resistance in the circuit will generate the most heat due to the higher voltage drop across them.

Best option would be as others suggested, get a standard fawcet from the hardware store, in this case, a "drinking water" type is what you need, they have a single connection, and single valve for controlling the cold water.

That devise on the end of your pump is the automatic pressure switch, place a standard toggle someplace, use it instead of the switch on the fawcet, then connect in series with the pressure switch.

If you use a faucet or any type of restrictor the pump with rapidly cycle on and off, you will need to create a buffer tank.

You can make an air buffer with a capped length of hose conneceted with a "T" or add a tank, also a hardware store item.

These are not expensive, and can be hidden in spaces that you would not normally use anyway.

If you make one out of a hose, it should all be "uphill", you want it to be full of air, then as the pump fills the system is compresses the air in the hose, so the amount of water in the hose is buffered by the pressure of the air, smooths out the pump operation, tank is better, but they cost more money and space, the hose can be routed into area under a bed, shelf or inside a wall.

336muffin · 10-16-2011, 01:08 PM

Quote:

Originally Posted by wa8yxm

Modern RV water pumps have a pressure cut off, but they are designed to provide water for a shower or a flush, not just a sink. Normally the sink has a valve that restricts the flow of water.

Cut into the line and put a valve in the line, adjust the valve so the water flow is... More within your liking. (That is the water line) don't drop voltage, that will cause other problems, restrict the flow of water OUT of the pump.

I like this idea because it is adjustable and much safer!

HHIDan · 10-16-2011, 01:16 PM

How about a pressure tank?

JimM68 · 10-18-2011, 05:01 PM

The resisters will be fine.

Tq60 has the math right, you need to refigure the current draw with the new resistance, it ain't gonna draw 7 amps thru 20 ohms.

No need to get overly fancy.