All standard Madden Pumps come with a flow adjustment knob. The flow rate is controlled by a lost motion mechanism. The adjustment knob controls the stroke length of the piston, which in turn controls the output of the pump. As the adjustment knob is turned down, the stroke length gets shorter and the output is lower. This design allows the flow rate to be adjusted while the motor speed remains at a constant speed.
Inside the pump body there is a flexible shaft that connects the adjustment knob to the stroke adjustment screw. This shaft rotates when the adjustment knob is turned, which in turn shortens or lengthens the stroke of the piston. Our pumps are designed to last for 20+ years with only simple repairs – replacing the flexible shaft is one of those simple repairs.
The video shown below goes through the process of replacing the shaft. To complete this repair, you will need a new flexible shaft (MP048) and a new rectangular gasket for the name plate cover. The steps are as follows:
- Loosen the set screws on the adjustment knob with an allen wrench.
- Remove the four screws that hold the nameplate/ adjustment dial to the pump body.
- Loosen the set screw at the bottom of the adjustable shaft where the shaft connects to the piston.
- Remove the flexible shaft from the pump body. If the shaft is completely severed, the top half of the flexible shaft may fall into the pump body. Be sure you have removed all the pieces before continuing.
- Connect the new flexible shaft to the piston by inserting it into the same hole where you removed the old one. Tighten down the set screw.
- To ensure your adjustment dial will be calibrated correctly, once you have the shaft connected to the piston, turn it clockwise as far as it will go. Next take the nameplate/dial and turn the adjustment knob until the dial reads 100.
- Next insert the free end of the flexible shaft all the way into the hole on the bottom of the adjustment knob. Make sure it is all the way in and then tighten the set screws on the adjustment knob.
- Put the new gasket on the nameplate and tighten down the four screws.
Madden Pump How to Replace the MP048 Flexible Shaft
Once you get your flexible shaft replaced, take a look at this previous post on dialing in the flow rate – https://maddenpump.com/adjusting-the-flow-rate-output-of-a-madden-pump/