Two machines side by side - bypass question

Hey all :slight_smile:

Short version of me requiring to make this post…

I have two GX390’s - one has a direct drive 15LPM @ 4000psi, the other has a reduction box and 18LPM (I think) @ 3000psi.

I tried the direct drive with an elevated buffer tank and bypass back to tank. It works, just low pressure. Can’t get over 3000psi. Attach to mains, 4000psi returns. I’m guessing that the direct drive doesn’t pull water, so the gravity fed supply is enough to work, just not forced enough for pressure.

I’d like to know if I can mains feed it, take the bypass to the tank - and then RETURN from the tank to the spare port on my inlet filter where the mains comes in?

I want to do this to use the tank as a radiator to cool the bypass water as opposed to going back to a short coiled hose which it had.

I wonder if the bypass, being fed mains pressure will just fill the tank, and the return from the tank won’t work unless the lid is on and pressurised… which is obviously not possible.

(The second machine will be using the tank feed as it sucks water just fine, unlike the literal direct drive).

Tanks in advance (yes, tanks!)

It’s my understanding that there must be something wrong with your plumbing between tank and pump if you’re not getting full pressure on gravity feed. But @Steve knows more about gravity feeding direct drive machines.

I don’t think you can use a buffer tank in the way you’re envisioning. The mains pressure will overwhelm the flow of water coming from the tank, and your tank will overflow.

The only way to do what you’re thinking of, is in a closed system, aka, an actual radiator that can hold mains pressure. I don’t know how many PSI a typical car radiator can hold, but I’ve always thought a small one would be pretty cool for a compact rig that doesn’t have the space for a buffer tank.

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Thanks for such a full reply. Much appreciated. That’s what I was thinking, pressure build up :frowning:

I’ll have to have a long bypass hose again and use the tank for the other machine next to it.

You saved my back from some leaning over today!

Oh, the plumbing seems to be the best it can be…

That’s 19mm oops! 3/4” feed direct to the pump.

Here’s another option, since you’ll still be using a buffer tank for your other machine:

Run the bypass on your direct drive through a coil of copper tubing. Submerge the coil in the buffer tank. Now you’ve got a quick and dirty heat exchanger/radiator for the direct drive.

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That’s thinking material for sure!

Based on the diameter of the pipe, the length and the water displacement - how much water volume will I lose from the tank?

Ha ha. Joking, of course!

Cheers mate :+1:t2::+1:t2::+1:t2:

Haha, not at all where I thought you were going with that question.

Your question is quite easy to answer. pi * r^2 * length.

What I thought you were going to ask is how much of a temperature drop you could achieve. To which I would’ve replied, “Beats the heck out of me :man_shrugging:.”

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I had to look up what the asterisk was for. Why do things have to change? People use periods between the area code and city exchange now on phone numbers instead of hyphens.

Using an ‘x’ for multiplication gets confusing in algebra, when it’s also used as a variable. So it’s notated with a small ‘•’. But in computer language, they needed to use a more common character to take the place of the bullet point. The asterisk has been in common usage for quite awhile now. Get with the times, man :stuck_out_tongue_closed_eyes:

The periods between area code and phone number is stupid, though. Makes it look like a really messed up IP address.

And I can’t stand the hashtag craze. It’s the pound sign, unless you’re writing code. Then it’s a hashtag


I have no need for algebra, ip addresses, bullet points or hashtags. I have accepted Facebook though.

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if you had a check valve leading from your buffer tank into your supply line, your idea should work. Never seen it plumbed that way, but cant see why not.

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That’s a European thing that’s beginning to catch on.

Thought I’d update the post.

I decided to use the straight direct drive machine for chemical application only, so I just made a long bypass hose. It will suffice for now.

The other machine has a higher flow, so I’ll use that for flat work and rinsing. (This one will use the buffer tank as it sucks water like crazy in comparison to the non-reduction box one).

I’ve made a two-way mains feed, one to the tank, one to the direct drive inlet. Controlled by taps so I can use both machines without changing anything.

I’ll also use a three-way ball valve to allow me to use the same high pressure hose and reel for both machines.

Thanks for all the help everyone :+1:t2:

Hey, question, what type of trailer/vehicle is your equipment housed in? Just curious

Hey, it’s an enclosed trailer…and I tow it with a small van for the surface cleaners etc.

One is for chemical app, then I switch the mains inlet, and a three way ball valve (so I can use the same hose and reel) to the other and use that for flat and rinsing as it has a higher flow.

It will be handy if I have break downs too, as I can switch immediately and finish the job.