Silencer Air Blower Question

[dmh]

10K gallon pool with attached spa. All Pentair equipment.
I am having an issue with my Silencer Air Blower (1.5 hp), as follows:
1. Turn on spa. Works perfectly.
2. Turn on air blower. Works perfectly.
3. Turn OFF air blower. Bubbles continue at about 20% the usual rate even the blower is off.
4. Turn off spa (switch to pool). Bubbles stop.
5. Turn spa back on. No bubbles until I turn on the blower again.
There is no air in the pool pump.
It seems like an air leak from the Air Blower when it is turn off. Is there a check valve in that line? Perhaps it is not closing completely until the spa is switched over to the pool? I am having trouble finding an exploded parts view for the Air Blower to see what is in the Air Blower housing.

 

[ajw22]

No check valve often in air line and no need for it. I think you are seeing a venturi effect with your water flow pulling air in from the air line even when the blower is off. Is it really a problem for you?

 

[dmh]

Only in that I have had the same pool equipment for about 8 years and never saw this before. The "after-the-fact" bubbles just started in the last week or two. I haven't done any major repairs to the pool equipment for at least a year or two, so that is not the answer. Has anyone else seen this happen?