Yes — this is a fairly common (and annoying) issue with multi-motor gutter vacs, and it’s usually not actually water-related at all.
What’s happening is almost certainly airflow/pressure related, not moisture.
Why the water shut-off valve is triggering
That “water stop” (float valve) is designed to rise when airflow drops or pressure changes, not just when water enters. When you run 2 or 3 motors, a few things can cause the float to lift:
1. Too much suction / pressure imbalance
When multiple motors engage:
Air is being removed faster than it can enter
A partial vacuum forms inside the barrel
This pressure difference can lift the float valve, even bone-dry
This is by far the most common cause.
2. Insufficient airflow into the drum
Even without blockages, this can happen if:
The hose diameter is too small
The inlet port is restrictive
Filters or mesh screens are partially clogged
The lid seal is too airtight
More motors = more demand for air.
If the system can’t feed them, the float reacts as if the barrel is “full”.
3. Float valve sticking or becoming over-sensitive
After months of use:
Dust, fine debris, or moisture residue can make the float move too freely
The guide shaft can become sticky or misaligned
The float may be slightly warped
This makes it trip early, especially under high suction.
4. Filter restriction (even if it looks clean)
Fine dust can clog filters invisibly.
With one motor it’s OK — with two or three, airflow drops enough to trigger the float.
Things you can check / try (in order)
✅ 1. Run it with the lid slightly cracked
Just as a test.
If the problem disappears → airflow restriction confirmed
✅ 2. Inspect and clean the float assembly
Remove the lid
Take out the float
Clean the shaft and housing
Make sure it drops freely under its own weight
No oil or grease — dry only.
✅ 3. Check for airflow restrictions
Hose kinks
Narrow adapters
Blocked inlet
Internal baffles clogged with fine dust
Even a 10–20% restriction can trigger this with multiple motors.
✅ 4. Check or temporarily remove the filter (test only)
Run briefly without the filter
If it behaves normally → replace or deep-clean the filter
✅ 5. Reduce motor staging
Some gutter vacs:
Aren’t designed to run all motors simultaneously
Expect staged airflow or larger hoses when using multiple motors
Manufacturers don’t always make this clear.
