Connecting two machines

Hey guys,
I have a questions for you, I tried hooking up two machines the other day, a 5.5 gal 3500 psi hot water skid and a direct drive 4/4000. I have a whip line coming into a t from each machine with check valves. The check valves are going in the right direction and the 4/400 was hooked to the house and the 5.5 was pulling from a tank. I tried adjusting the unloaded on each with no success. The skid was going into bypass when both machines were on, unless I started the skid pulled the trigger then had my help start the 4/4000. Then all of a sudden boom 9.5 gpm give or take half a gal I assume. As soon as I let go of the trigger though the skid would go right back into bypass. How can I fix this? There are a few jobs when getting that high will really help and it’s a nice tool to have in my bag.

Sounds like your skid has a flow controlled unloader on it. A siamese hook-up kit will not work with flow controlled unloaders or trapped pressure unloaders with the easy start feature.

You have to have both machines running the same psi, when you start the 4000 psi it’s pushing on the 3500 and will not let the check valves open.

Also to get the true 9.5 gpm you will have to step up your hose to 1/2"

We have run a bunch of miss matched tandem machines in the past. The only common thread that made them work was what Russ said. Trap unloaders.

I don’t think that we have ever even used check valves.

Forget about the half-inch hose for now. That stuff is too stinking heavy and hard to handle.

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But think about this Matt. If you’re using a nozzle for 8 gpm @ 3000 psi, the one machine won’t see 4000 psi.

Tim, the check valves aren’t a necessity because a trapped pressure unloader has one built in to the outlet, but they are a fail-safe should something happen to one or the other.

Hoe much are the kits to do this?


Thanks for that Russ. I was not aware of that. That does make a lot of sense.

Thankfully we have moved on from that. Now we soap with an 8 gpm and rinse with a 10 gallon per minute machine.

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I’ve messed with it a few times now and still can’t get it working, even with a new unloader, the one with the green spring. Thanks for the info all…

Pete, the one on your direct drive should be a pressure trap, the green spring one you have looked like a flow…so that’s why it’s probably not working.