4 GPM after stops but only 1.3GPM from rain shower head

[Dward0]

I just finished a shower remodel this week and the brand new no-name valve and 10" rainfall showerhead from Homary.com which advertises 1.8GPM is only delivering about 1.3GPM. I flushed the pipes before installing the showerhead, so I don't think there is any debris in there. Also I am getting nearly 1.6GPM out of the hand shower that is plumbed to the same valve. I measured the flow from the stop valves in the vanity sink which is on the same line and I am getting 4GPM there. Any suggestions on how to get more water or more velocity out of the rainfall shower head?

 

[Sylvan]

No name brand?? NOT a great idea. Check to see if there is a flow restrictor as REQUIRED by model codes

 

[Sponsor]

 

[Terry]

Are you measuring GPM from the shower arm or from the shower head?
The shower heads will have a flow restrictor, usually right where it threads to the arm. Those can sometimes be removed or tweaked with, (drilling a small hole) You didn't hear that from me though.

 

[Jadnashua]

First, a rainshower head isn't designed to speed up the flow of water...it is designed to just let the water fall out via gravity. Getting more volume may not make it any faster coming out of the actual head outlets. Only when there's a restriction in the nozzles (not upstream from them) will the water be accelerated according to the Bernoulli principle.

So, it appears that there's a bit more restriction TO the rain shower head. The volume outlet is mandated to NGT 2.5gpm nationally, so if yours is outputting 1.6GPM, you can still legally tweak it by removing some of the current restriction (i.e., a slightly larger hole through the restrictor). Some are designed to meet local restrictions that could be lower than the national code. Before you tweak it, you'd need to verify what the local code calls for. CA has a more restrictive requirement, and some companies don't want to carry different models for different states, so it may have been designed for there.