Loud brass valve - how to make it quieter?

Question

I have a 0.5hp pond pump, powering my backyard water features. My pump is actually very quiet - quieter than the natural sound of the running water, so you don't notice it.

The pump circulates 960 gallons per hour (16 gallons per minute) at a maximum pressure rating of 55psi - which is more than enough to run my two waterfalls (which dump into a shared pond).

(I also have a 1 gallon canister filter in front of the pump, so the pump gets clean water input.)

My pump has 1-inch female NPT/IPS ports, where I have screwed brass fittings.

The pump sucks water out of the pond, simple enough.
The pump sends water into a brass t-joint, splitting the water flow into two pipes, with one pipe feeding each waterfall.

The two waterfalls are at different elevations (about 24 vertical inches difference), so the lower waterfall naturally receives almost all the water flow by default, and the upper waterfall receives effectively zero pressure.

So I installed a simple brass valve into the pipe feeding the lower waterfall, which I can partially close on a permanent basis, restricting water flow to the lower waterfall, and forcing some pressure to be diverted to the upper waterfall.
By carefully adjusting this valve, I can dial-in exactly the correct balance of pressure/flow between the two waterfalls.

This is working great.
However, as the title suggests, this partially-open valve is making a LOT of noise - much louder than the pump itself, and louder than the running water, so it's impossible to ignore and very annoying.
I tried a ball-valve first which was very loud, and then I tried a gate-valve which was about 2/3 as noisy - an improvement, but not good enough.

What is the best way to make the valve quieter?

• Is there a different type of valve/regulator I should use instead of simple brass valves?
• Or can I wrap the valve in sound-absorbing material with adhesive? (Must be waterproof and outdoor-rated.)
• Or is there something else I can do?

Answer 1

A "globe valve" would be more suitable for the task. Both ball valves and gate valves are intended primarily for shutoff - either fully open, or fully closed.

A likely noise source is cavitation (bubbles forming and then collapsing) at the sharp edges in the flow when partially open. A gate valve has a plate with a (relatively) sharp edge that will be in the flow if partially opened, as does a ball valve.

A globe valve is more oriented to regulating flow at points between on and off. The opening is a ring that gets larger as the valve opens, without having part of the pipe wide-open for direct flow while another part is occluded by a sharp metal edge. There IS a sharp edge there, but it's presented equally to all the flow, and the valve design slows the water going through the partially opened valve.

You could also try running all the water to the higher waterfall, and putting the valve to feed the lower waterfall there, since you have excess pumping capacity. The additional pipe distance (friction head) to the lower fall and having already pumped up to the higher location would reduce the imbalance between the flows if they were split at this point, rather than at the lower falls. With some experimentation, you might also try a smaller diameter pipe to feed the lower falls, creating additional friction head (attempting to balance the additional 24" in real head to the upper falls, or at least put less of that job on the valve.)

Valve images are from wikipedia

Answer 2

What if, instead of hacking a valve to do something it shouldn't, you put a diaphragm (pressure reducer) inline with the lower waterfall feed, and adjust until you get the desired relative flow rates?