OT - Hydraulic pump rebuild

I have a Daikin V38A2RX-95 pump on my hydraulic unit. It operates at 1200psi. The pump is quite normally, but will periodically make what i would describe as a "pang" noise that resonates through the system and decays in volume for about 10 seconds. Then it will be quite for 20-30 seconds (or a few min) then make another "pang" that dissipates. Otherwise it functions fine, and I believe this is not a new sound, just new ears.
What I know:
-I am not sure that the sound is related to pressure demand, but it stands to reason, so maybe something related to internal bypass?
-It seems to have enough fluid in the tank, i.e. sucking in air was my first thought.
-There is a weeping leak under the pump that I do not think is related to the sound.
-All I could find was this diagram, but on page 2 these are some cutaways for the V38.

https://www.daikinpmc.com/en/catalog/GK247A_A-040SB.pdf

Does anyone have experience with hydraulic pumps/systems that might know where to start looking? I focused on the pump since the sound seems most intense there and at the outlet.

Thanks!

Cavitation or pressure spikes are the first things that come to mind, but that depends on several factors.

What valves do you have?
Where are the relief valves in the circuit?
Is the sound occurring under load or at idle?
Do you have a digital pressure gauge to watch for shocks/spikes? (Glycerin is too slow, shocks can happen in milliseconds and go waaay over the relief valve setting.)

Does the system involve moderate or long runs of steel hydraulic tubing that may be banging as some device slams closed. A "pang" in my mind is a hollow, tinny sound..not something really hydraulic sounding in nature. Just my WAG!

Stuart

Well this pang is hydraulic sounding. Like a valve opening hard. But attached to a spring that vibrates ??

Doesn’t really involve long runs and it happens at idle so I can’t tie it to a specific actuator.

Is this a load sensing closed center system ?

Why on earth label this post OT?

Well I’m not sure about load sending and closed center. The data sheet says it the “A” in the PN stands for pressure compensating control, and I had read that the flow auto adjusts through the pistons cylinders to meet demand.

I guess it’s not OT, just wasn’t machining specific so I wanted to play it safe.?

vmipacman said:

Well I’m not sure about load sending and closed center. The data sheet says it the “A” in the PN stands for pressure compensating control, and I had read that the flow auto adjusts through the pistons cylinders to meet demand.

I guess it’s not OT, just wasn’t machining specific so I wanted to play it safe.?

Click to expand...

Sounds like a closed center system.
Do you have an accumulator nearby ?

vmipacman said:

Doesn’t really involve long runs and it happens at idle so I can’t tie it to a specific actuator.

Click to expand...

Stupid question, but is there a mechanical overload valve or port that's being opened, and the "pang" is the shock of actuation, then as the valve closes it fades?