Stenner pump - low flow


Gold Supporter
Nov 15, 2015
Richardson, Texas

I have a Stenner 45MP3 that by my calculation should pump about 2+ ozs per minute... maybe slightly more. I installed it at the beginning of this season as a chlorine pump when we remodeled the pool. Typically my filter registers ~12psi though depending on rain, dust and other factors can go higher before I backwash.

I've had trouble regulating the chlorine most of the season. I'm in the Dallas area and now in June am running the pump 30 minutes per day and still chlorine goes very low and I have to supplement. I'm perplexed!

Today I pulled and inspected the injection valve (no check valve/duckbill) which is installed downstream of the filter and in the main line headed back to the pool. There was very little buildup - pretty much an open throughput. I checked both the intake and output tubes and found the same. I pulled the suction filter thing from my chlorine tank and found it clean. The white pump tube seems in good condition and pump rotation appears functional and adequate.

Finally I disconnected the suction tube from the tank and rigged a short length into a measuring cup with water. I ran the pump one minute and it barely depleted 1/4 ounce. I then disconnected the supply tube (to the pool plumbing) and ran a short length just to open air so I could test flow without the pump pressure.. I ran the pump for one minute and voila! It depleted over two ounces. So I believe the pump is functioning okay.

Question: If my injection valve is clear and the filter pressure is only 12 psi I'm struggling to determine why I have a low flow rate when connected to the injection valve and pool plumbing. Tubes are clear, chlorine tank suction filter is clear, injection valve is clear.

If anyone has had a similar issue please let me know. Even though everything says I don't need the check valve would it help increase my flow rate?



In The Industry
Jul 20, 2017
Windsor, Ontario. Canada
hummmm. That's a weird one Sam337.. You would think the Stenner hasn't enough pressure but they do. The check valve won't help in this case as it will still need the pressure to push it open. Just a guess as i have not had that issue with mind, but i would pay attention to the pressure on the rollers and the tube. At one time on a tube change i had very little output and discovered i had not released the roller fully. Not sure how i screwed that up but i locked them back and released them again and all was ok. Can the rubber on the tube get to hard and cause this, i'm not sure. Be sure you have no leaks inside the head coming from the tube as the pressure will take the easy way out. Good luck.


Silver Supporter
Mar 20, 2017
DFW - Plano, TX
Wow I have butchered this reply... ;) Sorry.

Just up the road a bit from you. We have similar pool characteristics. Pressure has been consistent 12-14. Like you we installed a Stenner this spring. No check valve as well. We haven't experienced your issues though. The pic below shows our injection point. Its using an old puck feeder port. Is your injection point horizontal or vertical? Not sure its critical one way or the other. Horizontal seems to work for us.
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Well-known member
Mar 4, 2015
Sugar Land , TX
You said it is a new install ? Did you supply your own tank? Did you drill a vent hole in the tank ? If yes, check vent hole to see if clogged. Also remember retail bleach is 6% now.


Gold Supporter
Nov 15, 2015
Richardson, Texas
Thanks all for the input and feedback.
1Sammy: The rollers and tube appear fine but I'll check if anything looks out of whack with the roller pressure.
Kirby: My injection port is on top of the return pipe so vertical. Thanks for the photo!
rphpool: Yes it's my own tank. I drilled a hole through one of the caps for the suction tube and rigged a sleeve of sorts. It's not a 100% airtight seal so I think venting should be okay but I will double check.

I'm also going to make sure my existing supply tube from the pump isn't clogged somehow - I hadn't considered this when using my short "temp" tubes to do the testing.

Bama Rambler

Mod Squad
TFP Expert
Bronze Supporter
LifeTime Supporter
Jun 22, 2009
SouthWest Alabama
As 1Sammy posted, check the rollers. I did the same thing once and it would pump and the compression on the tube looked right, but the rollers weren't released completely so if there was any back pressure on the discharge side it wouldn't pump to rated output.

You may need to collapse and expand the mechanism a couple of times before it "clicks". And it will be a distinct click when they expand correctly.

As for whether the pump tube can flatten, Yes it can, but they usually last a few years before that happens.
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