Dampening piston pump pulsation and sound

[Per Eriksson]

Anyone have any experience with piston pump pressure pulsation dampening to reduce the noise and vibrations in the hydraulic system and machine?
The machine in question has a double axial piston pump, 2x400l/min and a max of 35000kpa
sound is worst around 1500rpm.

What I have gathered so far is that it can be done in basically 3 ways,

Bladder accumulator installed on the pressure line so the flow goes in and then out of the acc.
Not too big but have moving parts which could fail and end up messing the rest of the system up.

"silencer", like a big steeltube that the flow passes right through, no moving parts inside which I like but very bulky and difficult nearing impossible to fit 2 of them in the machine.

"Dead end" hose, short length of hose T eed onto the pressure line.
Very easy to fit, cheap and no moving parts.

I'm leaning towards the dead end hose since that is something I have seen on other machines atleast in the caterpillar lineup but how the hell does the calcuations for them work, is it trial and error until the right length and size is found?

Anyone messed with this?

 

[lantraxco]

The stub hose is basically the same as using an accumulator, except you have to tune the hose length so the small amount of hose expansion matches the frequency of the pulses. The math is years above my high school algebra level I'm sure. Small high pressure accumulators are easy and mostly foolproof, you still have to tune it, but that's done by varying charge pressure for best result. YMMV

 

[John C.]

Komatsu uses the snubber hose on all their excavators. You might find a machine in the same model size and start with that length and diameter of hose. There is something special in what they do though. I've had to tell people many times that going down to the hose and fitting place will not work the same and that the hose will fail long before the manufacturer's hose will.

 

[excavator]

I think this will be an interesting thread. I have a customer who bought a fairly new Gehl telehandler and at a certain RPM the pump noise will almost drive you out of the cab. I talked with him about the accumulator or the stub hose and haven't heard back. Never occurred to me about the hose length, Deere/Hitachi also use them on their excavators and I probably know of at least 5 or more older machines that have them removed and to be honest with you I can't tell the difference. Not that I'm deaf or anything.

 

[Nige]

Regarding accumulators is a piston accumulator also a viable option..? A piston accumulator is far more reliable than a bladder type in my experience.
I'm thinking something along the lines of the 241-3147 HARC accumulator on large mining trucks. It's only 15" long overall and 3.5" diameter. See photo.

Bugger - maximum working pressure is only 3000psi (20700 kPa).

 

[Per Eriksson]

Piston accumulator isn't recommended since it will only move a little but with high frequency and the seal will make a wear spot in the wall.

Think we'll start by fitting a t block and from there it's easy to run a stub hose or accumulator and hope we'll get lucky on the sizing.

 

[John C.]

Snubbers run at system pressure which now days is in excess of 5,000 PSI. You are only trying to take out the resonant vibration set up inside the pump at the dividing line of input oil and discharge oil. They also work for the pressure spikes that are too fast for a relief valve to react to.

 

[lantraxco]

Regarding accumulators is a piston accumulator also a viable option..? A piston accumulator is far more reliable than a bladder type in my experience.
I'm thinking something along the lines of the 241-3147 HARC accumulator on large mining trucks. It's only 15" long overall and 3.5" diameter. See photo.

Bugger - maximum working pressure is only 3000psi (20700 kPa).

View attachment 229790View attachment 229791

Right, piston type accumulators are more rugged than bladder style, but are designed to cycle over a fair percentage of their stroke. For dealing with pulsations the bladder style has a lot less moving mass and as Per said oscillation without cycling will create wear spots in the tube.

 

[lantraxco]

I think this will be an interesting thread. I have a customer who bought a fairly new Gehl telehandler and at a certain RPM the pump noise will almost drive you out of the cab. I talked with him about the accumulator or the stub hose and haven't heard back. Never occurred to me about the hose length, Deere/Hitachi also use them on their excavators and I probably know of at least 5 or more older machines that have them removed and to be honest with you I can't tell the difference. Not that I'm deaf or anything.

Well, it's likely the snubbers that were removed were not originally intended to eliminate noise so much as reduce damage to system components like pump internals and valve spools. Say you have a piston pump with 9 pistons turning 2,000 rpm to keep it simple, that's at minimum 18,000 pulses per minute or about 300 hz. It's possible that you get a pulse at either end of the pumping cycle on the valve plate, and if you have multiple pumps that are even a tiny bit out of sync, you get multiple wave forms in the fluid and let's not even get started on harmonics and sympathetic vibration of steel tubes and the more flexible hoses. Then pressurize it up around 5,000 psi... kind of a wonder any of this stuff lives long, but then that's what we pay engineers for, eh?

 

[Volvomad]

How many times have the engineers ft up their algebra .I know nout about harmonics but I stuck either a bladder or diaphram accumulator (one I had lying around) on a closed centre radial piston pumped deere tractor one time and it seemed to make a big difference .Then anything would have been an improvment on them auld yokes . We have always had a love,hate thing going on.

 

[lantraxco]

How many times have the engineers ft up their algebra .I know nout about harmonics but I stuck either a bladder or diaphram accumulator (one I had lying around) on a closed centre radial piston pumped deere tractor one time and it seemed to make a big difference .Then anything would have been an improvment on them auld yokes . We have always had a love,hate thing going on.

I agree, the Deere radial piston pumps were actually a wonderful thing, very robust and efficient... the systems the engineers plumbed them up to often were shall we say, something less than wonderful?