Grundfos CMBE Booster Pump

[Kantdaddy]

I have a CMBE 5-62 installed in my crawlspace. It is on city water, but with low pressure. Lately, the pump is running intermittently when there is no water demand. It runs for 6 seconds with 21 seconds of rest. so, basically all night long it runs for 6 seconds, every 30 seconds.

What could be causing this? Could it be a very small leak? Maybe a drip from a faucet? Any ideas?

Thanks in advance!

 

[Valveman]

You most likely have a leak. That little tank can't hold a 1/4 of a gallon of water, so you have maybe a 1/2 GPM leaking somewhere. Could even be the check valve leaking back, which is common on those variable speed type systems. Are those little booster systems really 3,000 bucks? A $500 regular jet pump with a $395 PK1A to make it deliver constant pressure would have cost 75% less and worked 100% better.

 

[Sponsor]

 

[Kantdaddy]

You most likely have a leak. That little tank can't hold a 1/4 of a gallon of water, so you have maybe a 1/2 GPM leaking somewhere. Could even be the check valve leaking back, which is common on those variable speed type systems. Are those little booster systems really 3,000 bucks? A $500 regular jet pump with a $395 PK1A to make it deliver constant pressure would have cost 75% less and worked 100% better.

Thanks, Valve! They are expensive but I think I got mine for under $2k. Still too much. I had a $500 booster pump that failed and replaced it with this. It really is a lot better than the previous model. The old one had to drop pressure before it would come on, this one just comes on with demand.

I will have to look into the return valve. I know I have a faucet that has a drip, but not very bad.

 

[Valveman]

It doesn't take much of a drip with a tank that size. But it is mostly because there is no drop in pressure before the pump comes on. That is important to get some water from the tank. Using a 4.5 gallon size tank that holds 1 gallon of water and letting it drop from 60 to 40 before the pump comes on will not cycle very often with a tiny drip from a faucet. When you really need water the drop in pressure happens so quick as you use the gallon from the tank that you don't really notice it, and then a CSV would make a regular jet pump hold constant pressure like those expensive variable speed pumps do. What you are describing is one of the usual problems people have with VFD type pump systems and is why we have been using Cycle Stop Valves to replace Variable speed pump since 1993.

 

[Kantdaddy]

Thanks! I will look into the CSV when this one fails.

 

[natelive]

I’m buying a house high on a hill and although it’s on city water supply, it has low pressure. The sellers have a hookup spot for a booster pump but say they took it out because it was loud and didn’t mind the low pressure. I’d like to boost the pressure after moving in and am wondering what to expect. I assume if I spend a bit more on the pump I can get a quieter one, and from googling around a bit it seems like some of them keep pre-pressurized water in a vessel to save the pump from coming on every time you run a faucet. What else should I look out for when shopping for one? Do they typically get hooked up before filters/softeners/heaters or afterwards? Also, there’s some talk of the city improving the water pressure situation “soon”, so what would happen if the inbound pressure improves? Will it harm the pump and make me take it out or will it just be less useful?

I haven’t closed on the house yet so I’m not clear on how it’s all plumbed today, but want to be prepared when the time comes. I’ll be getting it professionally installed but would rather get as much information as possible prior to hiring someone.

 

[Valveman]

You have about 4 options.

One is the old pressure tank/pressure switch pump control. This requires a large pressure tank and your pressure will be fluctuating between like 50 and 70 PSI all the while you are using water. The continual cycling on and off between 50 and 70 wears out the tank, switch, pump, check valve, and everything in a pump system. But this is the way it was done for a hundred years.

Your second option is to add a Cycle Stop Valve to the standard pressure switch/pressure tank pump control system. The CSV will allow the use of a much smaller tank, eliminates the cycling that destroys everything, causes water hammer, and the pressure to fluctuate between 50 and 70 over and over. The strong constant 60 PSI from the CSV will be much stronger shower pressure and causes the pump system to last many times longer than normal.

Third option is the variable speed pump like in this thread. They will deliver constant pressure and use a small tank. However, they are expensive, cause lots of trouble, and don't last very long. Much better for the people selling them than the people using them.

Fourth option is one of the many so called tankless controls. There are many different brands of these on the market. They use a flow switch to shut the pump off and pressure to turn it on. There are a multitude of problems from these type controllers, which again are much better for the people selling them than the people using them.

When using a 50/70 pressure switch, like when using a CSV to get a constant 60 PSI supply, the pump just will not come on if the city is able to keep the pressure higher than 50 PSI. The water will just go right through the pump. Only when the pressure is below 50 will the pump start and boost the pressure to 60 as is the setting of the CSV.