As the saying goes, Long-Time Reader, First Time Poster. Have an odd low pressure situation that I can't figure out, and haven't seen addressed in pool school or older posts.
I have an in-ground 18x36 pool that is roughly 25K gallons total. The pump is a Hayward Superpump 2607X10 with a 1HP A.O. Smith motor. Hayward sand filter, I forget the model but I don't think that's an issue here. Since I've had the pool, about 3 years now, the system has run at right about 20 PSI on normal operation.
Last week, the motor died without warning. I replaced it with a new motor last Monday, and then re-installed the old motor last Tuesday (The lesson here: Check ALL the electric connections before deciding that a motor is dead). Since that time, the pressure gauge is showing about 10 or 11 PSI consistently. It's possible the motor is running a little hotter than it used to, it's hot to the touch now and I don't remember it being that way before I swapped the motors, although it's possible I just didn't notice; in any event, it hasn't gotten hot enough to shut itself off. Subjectively, it seems like the flow out of the return is the same strength as it was before, but again, I can't say for sure. I have a Hayward gas heater installed after the pump. The flow into the heater is enough for it turn on, as it has a mechanism that prevents it from being turned on when the flow is too low (e.g., the pump is off, the baskets are too clogged, etc.).
I cannot for the life of me diagnose the cause of the low pressure reading. The baskets are clean. There are no obvious air bubbles visible in the strainer pot or coming out of the return. The impeller is clear and unobstructed. The pressure gauge drops to 0 when the pump is turned off, and it was replaced at the beginning of this spring anyway.
So one possibility is that the simple act of replacing motors has somehow altered the system such that normal operating pressure is now half of what it used to be. I don't see how that makes any sense, so I doubt it. The other possibility is that something is causing a low pressure issue and I'm missing what it is.
Anybody have any thoughts or insight?