Is my pump dying?

[TimS]

Last evening I noticed that the pressure gauge on my filter hasn't moved at all over the past month. Normal operating pressure lately has been 12 psi. I haven't had a huge problem with dirt lately, but I would have expected to see some movement. I replaced this gauge this spring, and was wondering if it had gone bad again. I started closing the outlet valve from the filter (valve in the line, not the multi.) As I closed the valve, the pressure slowly rose, but the sound of the pump didn't change at all. I finally closed the valve entirely, and the total pressure difference was only 6 psi (from 12 to 18) I know the valve was restricting most if not all of the water, because the water in the pump pot stopped moving. Still, the sound of the pump did not change. I didn't want to leave the valve closed and the pump running long enough to check the waterflow at the return, but it should have been very minimal or completely stopped at that point.

The normal pressure at the return seems lower than it was last year. This is subjective, since I don't recall what my operating pressure was last year, it just feels lower.

It doesn't appear to be a bad spider gasket, since I didn't get any flow through the backwash line, which would have been the only way out with the valve closed.

Shouldn't the pressure on a DYNII-N1-1 1HP get higher than 18 psi? Sorry, but I have no clue what my head is. The plumbing is 1-1/2". The total run from filter to return is about 14' with 9 elbows, total run from the pump to the filter is 3' with two 45s and one 90, and the total run from the skimmer to the pump is about 8' with 5 elbows, if that helps any.

 

[mas985]

With that setup, I get a normal pressure of about 12 PSI so that would be reasonable. If the suction side plumbing or impeller was blocked, then I would expect a drop in pressure but it would need to be a lot to go to zero. Before the gauge went to zero, where you cleaning the pool or opening?

 

[TimS]

The pressure didn't go to zero because I didn't try turning off the supply. The issue is that the pressure doesn't climb as high as I would expect.

 

[JohnT]

Your pump is going to turn at pretty well the same speed all the time, and the impeller is going to move the same amount of water with the same motor speed. If something had cause your motor to slow down, I'd expect you'd be seeing more problems than what you are seeing.

You shouldn't be able to see if the water in the strainer pot is moving or not. If there is air in there that lets you see the water move, get that fixed and I bet you will solve your problem.

 

[TimS]

Because of the way the lid is made, there is always a small bubble at the top. The lid is a dome shape, and due to the ribbing on the lid, there is a circular cavity in the ribs in the center of the lid about 1/2" across and 1/2" deep that always has a small bubble in it. I'm not leaking air anywhere.

Let me rephrase a bit. I'm not seeing the water itself move. What I'm seeing is the small stuff that gets picked up by the skimmer, and the movement of that small bubble.

No the motor speed is not changing, and I don't expect it to. I would kind of expect the pitch of the motor to change as the pressure increases, and I really expect the pressure to increase more than 6 psi and to a max pressure higher than 18 psi with the filter outlet restricted.

Also, there are no restrictions in the intake line, and water is flowing freely through it. The pump is certainly not sucking air, nor is it starved for water.

 

[mas985]

Ok, I think I understand a little better what you are explaining. First, maximum head for that pump is about 55' so maximum pressure would be about 23 PSI when the return valve is completely closed off (i.e. dead head). If you are saying that it only rises to 18 PSI, then there could be clog in the impeller. This would lower the PSI in normal mode as well as if you block the return side.

Second, when you shut off the return side, the pump noise should decrease as you are reducing flow rate which causes most of the pump noise. So that is consistant.

 

[zea3]

I have the same pump, but I usually do not have air at the top of the pump basket. It only collects air when the water level is low in the pool, or when the strainer basket or filter need to be cleaned.

 

[TimS]

Mas,
I don't suppose there's any way to check for a clog without disassembling the pump? I could always replace it with my spare and see what happens.

Zea,
I'm not at all surprised that I have an air bubble in the lid. The way the lid it built, at the top of the dome, at the center of all the ribs is a circular cavity about 1/2" across and 1/2" deep. In addition, there is a spike in the center of that cavity, probably from an unremoved relief passage from when the lid was poured. It's in this cavity that the bubble develops. The bubble is only about 1/8" thick. As far as I can tell, there is no way for the water to displace the air in that cavity, since there's nowhere for the air to go after a certain point. When the lid is full of air (after opening, for example,) I can see the water displacing the air as the air is drawn through the pump. Once the majority of the air is gone, I can see it slowly pulling small bubbles off the bottom of the bubble in this cavity. After a point, there is not enough water movement in that cavity to draw the air out of it. The way the pot normally fills, if that cavity wasn't there, or there were a way for the air to escape from it, there likely wouldn't be a bubble at all. As it is, I've never seen that bubble disappear. Note that there are no other bubbles in the lid, only in that cavity. Once the pot is closed, no new air is introduced, and no new bubbles appear anywhere.

Attached are pictures of the lid, and the bubble.

Here's a pic of the lid. If you look closely, you can see the spike to which I refer.

Here's a pic of the bubble in the lid. You can just make out the edge of the bubble in the center, along the bottom side of that center ring.

Are you saying that your lid has the same dome and circular cavity in the center with a spike in it, and the bubble disappears from yours? I'm being specific about the spike because the other lid that I have looks exactly the same, but the spike has been cut out of it. Unfortunately, that one DOES leak, even with a known good o-ring. From the different way the water moves through that cavity, I would expect the bubble to disappear if that lid was not leaking. It's also conceivable that if I never shut the pump off, the bubble that I have would go away too, but the pump is on a timer and doesn't run 24/7.

At any rate, I'm not concerned that the bubble I have is indicative of an air leak.

So, the real question is, Is there any way to check for a blockage in the impeller without disassembling the unit, or is there anything besides a blockage (or an air leak) that would cause a low pump pressure?

 

[mas985]

I don't suppose there's any way to check for a clog without disassembling the pump? I could always replace it with my spare and see what happens.

Sometimes you can reach through the pump basket into the inlet and feel if there is anything there.

I've never tried this but if you can get to the return side of the pump and force water backwards through the pump with a hose and the pump lid off and basket out, it might dislog something that could be caught in the impeller.