Pressure Trap vs Flow activated unloader.

Michael T

Member
I just acquired a RK40-c skid. I bought out another contractor. It has a clutch on the pump and a pressure trap unloader.
I really dont like pressure trap unloaders for several reasons. So I wanted to convert to a K-7 unloader. I contacted the manufacture technical department with the question. " Can I change out the unloader and still keep the clutch? And will it all operate the same?" The short answer was No. But no one had actually tried it yet.

Being left handed, right brained, reverse engineering, Macgyver type guy I am. The wheels started turning. This type system requires 2 pressure switches, one for the fuel and one for the clutch. Without to much technical discussion. The fuel/burner needs to be on during flow and off in bypass. And the Clutch need to be off in bypass and on during flow. It took me about 2 hrs to reconfigure, because it is inside a van and I have big hands working in a tight space.

Conclusion: Success, It works flawlessly, just as designed, but with a K-7 unloader instead of a Pressure trap unloader.

Now we have much more control of the wand working in tight quarters ( like in KEC applications ). The only draw back is the burner flow switch needs 750psi to activate. Sometimes we need an open gun to rinse with hot water. This is not really much of an inconvenience. I really love these type of challenges.
 
I just acquired a RK40-c skid. I bought out another contractor. It has a clutch on the pump and a pressure trap unloader.
I really dont like pressure trap unloaders for several reasons. So I wanted to convert to a K-7 unloader. I contacted the manufacture technical department with the question. " Can I change out the unloader and still keep the clutch? And will it all operate the same?" The short answer was No. But no one had actually tried it yet.

Being left handed, right brained, reverse engineering, Macgyver type guy I am. The wheels started turning. This type system requires 2 pressure switches, one for the fuel and one for the clutch. Without to much technical discussion. The fuel/burner needs to be on during flow and off in bypass. And the Clutch need to be off in bypass and on during flow. It took me about 2 hrs to reconfigure, because it is inside a van and I have big hands working in a tight space.

Conclusion: Success, It works flawlessly, just as designed, but with a K-7 unloader instead of a Pressure trap unloader.

Now we have much more control of the wand working in tight quarters ( like in KEC applications ). The only draw back is the burner flow switch needs 750psi to activate. Sometimes we need an open gun to rinse with hot water. This is not really much of an inconvenience. I really love these type of challenges.

What happens with a k7 if you restrict the flow with a ball valve or a smaller tip?

Sent from my DROIDX using Tapatalk
 
Using a smaller tip will cause a K-7 to go into bypass. On-Off-On-Off-On-Off it will kick in and out of bypass. With a K-7 it is either on or off. There is no leaking into bypass like with a pressure trap. To change the pressure, change the tips. What we also use is a showerhead tip. It drops the pressure at the tip by bypassing around the tip. You still have the same flow (GPM) but the water is diverted around the tip.
 
The RK-40C is a nice little machine. I am not a fan of flow unloaders, because I feel like they are less reliable, but then, everyone has a different opinion. I can't see any reason why it would not work the way you have it set up.
 
Where are the pictures of the cool rig?
 
just go to a flow-switch for heat..
your output pressure will be adjustable without kicking off the heater.
.. and ..
your heater will be SAFER..
the heater will ONLY go on, when you have actual "FLOW"..
like it aught to be,
and like I teach in my PressureWasher "BulletProofing" class. :{)
..Just make sure that all you're turning "on" with the switch is the fuel solenoid,
and if a 12 volt burner..
make sure you use the 3amp version Flow Switch.
 
K-7 retrofit to RK40C

IMAG0994.jpgIMAG0991.jpgHere is a pic of the setup.
Pic1: Rear of van with relocated pressure hose reel. Hose reels were originally mounted in side door. Inlet hose is still inside of side door.
Pic2: View of K-7 Unloader. The Pressure switch to the burner is on pressure line visable on the left slightly behind the pressure line. Pressure switch to clutch is on the right at pressure port right behind the bypass hose.

Jerry, Is there a pressure switch which activates at < 750psi ? I really dont like flow switches. The get sticky and glitchy, hanging up letting the burner run without flow. Anyway thats my experience.
 
ST-5 Flow switches

There are 360psi versions of the pressure switch.

When I refer to a flow switch.. I mean the ST-5 Suttner FlowSwitch..
It has to be mounted in the vertical position, but they are VERY reliable.
WAaaay more reliable than a pressure switch.

There are spring-loaded versions of the flow switch that are less reliable,
especially the spring-loaded ones, and those with the 1 amp reed-switches.
But follow my lead, and you're fine.
 
Last edited:
Back
Top