Buffer tank - pressure drop

Hey guys, I could really use some help here. I am almost done building my first setup and having issues with the pump delivering high pressure when fed by the buffer tank.

Some points to note:

  1. The buffer tank has a large opening at the top to allow air in
  2. When I connect a garden hose to the pump it works perfectly fine and I have great pressure
  3. On advice from this board, I removed from the pump inlet the garden hose connector F-GHT and installed a 3/4 NMP to a brass barb which connects to my 3/4" buffer tank supply line. Right or wrong I now have no way to connect a garden hose to the pump. I may rethink this later.
  4. The machine is a belt drive 4k/4 Simpson with a Honda GX engine
  5. With this issue, I am getting about 1 GPM and just no pressure. When I am off the trigger I do see the PW and the lines flex-up indicating a fair amount of pressure. When the trigger is squeezed I get one blast of pressure then it dies down to about 1gpm.
  6. I am using spa and hottub line which is 3/4" ID It’s pretty rigid and I’ve seen others use this line too.

The buffer tank is a 50 gallons which is not elevated but I have 30 gallons in the tank and the water level is deff higher than the pump.

I disconnected the buffer tank supply hose at the pump inlet and water does flow freely.

I made sure the 3/4" line from the buffer tank was straight with no 90 degree turns.

When I open the dump valve which I have on the supply line (seen near the filter) I am deff getting plenty of flow.

Getting frustrated with this issue, any suggestions?

In case it will help, here are the connections at the pump.

You need to start again mike, that’s a mess.

Start with a 1 inch bulkhead off the tank and a 1 inch nipple off the pump. Connect the 2 together.

The idea with waterlines, is to have the bulkhead of the tank higher than the pump, not the actual fill line.

I will also add, you don’t want to use that hose for the injector. It tends to collapse when hot. Get you some wire reinforced vacuum hose.

The unloader is the problem.

You have 14 possible air leak locations. That’s a lot. Do away with the T. Run 1 inch vacuum hose, not 3/4.

What he’s using is all I have ever used, even in box trucks and enclosed trailers.

Maybe, but I think he’s just sucking air and not getting water.

Yep, me too on the injector line.

My belt drive sits 30" above my buffer tank bulkhead and sucks like crazy.


You’re getting air in the system somewhere. Are you leaving your gun on long enough, to get all the air out when you start. Though once it’s primed should be good to go. Sounds like you have good flow, right up the machine just naturally and 3/4" line is plenty for a 4gpm machine. Try unplugging the injector and just let it shoot out side of pump and see what your flow is. Might be some restriction somewhere coming out. It’s just a process to keep eliminating stuff.

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Locks like build in unloader with internal bypass , maybe that don’t like gravity feed. What is that small hose barb on tap ? build in DS injector.

Your right Rick, for some reason I though this thing was a direct drive.

Supposed to gut the internal bypass unloader for flow, then add the proper unloader of choice, then dsi. But heck, it could be compounding issues.

Mine too. Not 30" but at least a foot.

Is the unloaded bypassing all your water into the tank when your on the trigger.

Try capping off the injector, it is possibly sucking air due to pressure drop. How many feet of hose do you have on the reel. Are you pulling the entire hose off? or leaving some coiled? If so, unreel the entire hose.

Many thanks guys on the feedback. I was out for the weekend or I would have responded sooner to thank you all. Based on Muscles’ initial feedback I did order the 1" barb / NMP connector for the pump inlet. Combined with Rick’s feedback I think my initial move will be to buy a fresh section of 3/4" hose and run it from the buffer tank into my existing 3/4" barb on the pump inlet. This will bypass the filter, the dump valve, etc. Doing this will tell me a lot about the issue I feel. From there I will add back filters and valves to see what happens.

I’ll keep the idea of the unloader being the issue in mind too but since the garden hose worked fine I wonder if the unloader can be blamed.

One item I thought about and would like some feedback is when I use PVC hose barb fittings (when applicable) the fit of the spa hose I have onto the PVC 3/4" barb is super snug. I need to heat up the hose to get it on and apply some soap. BUT, when I slip the hose on all of my brass fittings the hose slides over it super easy. I started to wrap the brass barb with teflon tape to make the diameter bigger and it does help to snug it up. Also, I double clamp all these fittings. This issue would certainly point to suction leaks.

Do you guys have the same experience with brass hose barbs noting being snug on hoses? If so, how do you handle this?

I hope to run the new direct line from the pump to the tank today and will post my results.

I’ll try this. I am only running 125 feet of hose but some of the hose was still on the reel. I will try to uncoil it and see what happens. I also thought about the injector built-in on the pump sucking air. I have some vacuum caps I will put on. Thanks!

I’ve had the same issue with brass and some poly barbs as well. Double clamping has worked for me no problem. One clamp on one side of the barb and one on the other so the clamping is spread out some.