Some of the Moen shower faucets have a balancing spool. If that bugger hangs up and does not shift back and forth it will cause problems. Take off the escutcheon and you should see a large straight screw driver slot on the right side as you look in. The spool is inline with the water line feeding your faucet. Shut off water and remove the screw slot with a large screw driver. When you take out the spool shake it back and forth. You should hear/feel the spool moving back and forth. If it does not move freely some construction debris( wood chips from pushing pipe threw drilled holes, or solder) may have gotten in there.
You can take the cap off the bottom and pull the spool out, clean it up and put it back together. Otherwise it's buy a new spool $50. Moen does not warrant this part.

quote:

Originally posted by trapper189:

quote:

Originally posted by Rustpot:

quote:

Originally posted by trapper189:
The recirculating loop is essentially a closed loop and pressure on each side of the pump should be equal whether the pump is running or not.

That's not true at all. If the pump is running there had better be more pressure on the discharge side.

Think about it for a minute or two if needed.

In a closed loop, where does the pressure on the discharge side go?

It drops via losses as water moves from high to low pressure. The pump will read the lowest pressure at the inlet and the highest at the outlet, given a simple closed loop.

Go put a pressure gauge on the inlet and outlet of a pump. If they read the same the pump is off. If the pump is on and they read the same something is broken as you physically can't move water without a pressure differential.

quote:

Originally posted by Balzé Halzé:

quote:

Originally posted by jimmy123x:
I have a 1 year old Moen bathroom faucet. If you turn it on full blast, after ten seconds the water goes down to 30% of the volume and it's the sink fixture. Try changing the moen shower valve as it's most likely the issue.

I have to agree with Jimmy. Sounds to me like the issue is with the shower valves.

It's either that, or if the house is plumbed with pex, there is a kink on the supply line to the 2 showers, it builds up enough pressure and there's enough volume in the line past the kink to run full bore for 10 seconds, but then the reduce flow presents itself. Like a garden hose with a hose nozzle that the valve is open only a little. Open the hose nozzle full bore and it will flow good for a short period of time and then pressure and volume will slow way down to whatever the valve is allowing the flow.

What was it? New cartridges?

quote:

Originally posted by Rustpot:

quote:

Originally posted by trapper189:

quote:

Originally posted by Rustpot:

quote:

Originally posted by trapper189:
The recirculating loop is essentially a closed loop and pressure on each side of the pump should be equal whether the pump is running or not.

That's not true at all. If the pump is running there had better be more pressure on the discharge side.

Think about it for a minute or two if needed.

In a closed loop, where does the pressure on the discharge side go?

It drops via losses as water moves from high to low pressure. The pump will read the lowest pressure at the inlet and the highest at the outlet, given a simple closed loop.

Go put a pressure gauge on the inlet and outlet of a pump. If they read the same the pump is off. If the pump is on and they read the same something is broken as you physically can't move water without a pressure differential.

Rustpot is correct. There will be a slight difference when the pump is in operation and pumping.

That's not true at all. If the pump is running there had better be more pressure on the discharge side.[/QUOTE]

Think about it for a minute or two if needed.

In a closed loop, where does the pressure on the discharge side go?[/QUOTE]
The pressure on the discharge side is dissipated by friction and the suction from the intake side. There may not be much pd but it is there...