Hi Dear All,
In a hydraulic system,an unusual vibration is observed.
The maximum amplitude of the vibration is observed in the pipeline.
The amplitude increases every 40 seconds for 7 seconds.(Picture)
There is only one Electro-Pump in this system and in this building.

What do you think?

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Photos (1)
Original Post

May be due to periodic pressure release through some valve that could be broken or not working properly (cocked valve). It is hard to tell without knowing exactly how the system works.

The issue could also appear due to some machine's operating cycle property, for example when hydraulic press gets in contact with the workpiece and the pipes aren't properly attached, they could resonate at some higher pressure.

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Becar posted:

May be due to periodic pressure release through some valve that could be broken or not working properly (cocked valve). It is hard to tell without knowing exactly how the system works.

The issue could also appear due to some machine's operating cycle property, for example when hydraulic press gets in contact with the workpiece and the pipes aren't properly attached, they could resonate at some higher pressure.

Thanks dear BECAR

We checked the valves, But we will check again anyway.

All machines is on standby. there is not any machines on operating cycle.

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Are you sure that the waveform is not time-scale in milliseconds? If it is then, 39 m-sec = 25.6 Hertz or equal to 1xSS of pump. Otherwise there is possibly a Water Hammer acoustic pulsation, but a repetitive pulse at 39 seconds interval would be highly unusual. How about a pressure or volume unloader valve internal or near pump? If machines are on standby and pump is on, then there should be an open recirculation path.

Walt

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Walt Strong posted:

Are you sure that the waveform is not time-scale in milliseconds? If it is then, 39 m-sec = 25.6 Hertz or equal to 1xSS of pump. Otherwise there is possibly a Water Hammer acoustic pulsation, but a repetitive pulse at 39 seconds interval would be highly unusual. How about a pressure or volume unloader valve internal or near pump? If machines are on standby and pump is on, then there should be an open recirculation path.

Walt

Hi dear Walt

Thanks

About time, I'm sure. (time length of all waveform, is about 174 sec)

Water Hammer acoustic pulsation is completely periodical? What we can do? what is Additional test for it?

I will check other parameters.

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Becar posted:

May be due to periodic pressure release through some valve that could be broken or not working properly (cocked valve). It is hard to tell without knowing exactly how the system works.

The issue could also appear due to some machine's operating cycle property, for example when hydraulic press gets in contact with the workpiece and the pipes aren't properly attached, they could resonate at some higher pressure.

Vibration changes are with 0.85 bar Pressure changes.

Working pressure is about 48 bar

Pump is PVH/350 Liter/250 bar

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Regarding this info I am quite sure there is an issue on the valves or in the leaking somewhere in the system. Maybe you should set the valves differently

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Becar posted:

Regarding this info I am quite sure there is an issue on the valves or in the leaking somewhere in the system. Maybe you should set the valves differently

How leaking or issue on valves,  increases the vibration to 10 times?

110mm/s is completely unusual!!!!

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100 mm/s is nothing unusual for some piping issues in industry. Vibrations at this level cause some damage soon or later. In most cases the reason is some source frequency resonating with some part's natural frequency. In your case there should be some recirculation bypass (as Walt said) otherwise your system would explode. The recirculation system should have some automatic pressure regulation valve. It should constantly (every moment) allow the oil to go through when the pressure exceeds the value set. But when the valve is cocked or broken, in one moment the valve can't allow the oil to go through until the pressure reaches some higher level. Then the valve is suddenly released and this shock pulse could trigger some piping resonance. That's only my guess, one of the probabilities.

You didn't send much data, my friend. Which machines are on the hydraulic system? Why machines are all on standby and although you are running the hyd. pump? Is the issue still present when you turn on the machines? What type of pipes? How are they installed? Any photos?

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Very few details provided so far....what the pump does in the system it is installed into, something moves from point a to point b, clamps something etc

As others stated vibration data is needed to assist in troubleshooting.

My take on your post shows a time waveform with unknown resolution. The rise in amplitude appears to be sudden, like a valve let pressure slip by and the pump started working to maintain system pressure for 7 seconds, then as the pressure bleeds off this happens again. You have to understand the system operation before you can say this is even an issue. Are you taking data on a pipe or the pump? piston/rotating vane pump?

What is the main issue you are having?

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I agree with Dave and others.

What is the dominant frequency during a single high vibration event? Is it pump pulsation frequency (or harmonic) or a natural frequency of the pipe? Water Hammer is not a periodic event, but each pulsation event may be amplified by fluid resonance and/or by structural resonance.

What to do? Start with the big picture and then focus, as needed:

Telescope
Binoculars
Normal eyesight -- possibly with glasses
Magnifying glass/lens
Microscope

Walt

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Thanks Dear Walt,Dave and BECAR

• In my case, vibration level of motor and pump are normal. (See Attached Picture)
• About resolution, I've attached a movie. (Base frequency in all time of signal, is motor speed and only amplitude is variable)
• This system is used to move a cylinder, In Our hydraulic system, we have one machine but Even when the machine is off, there is vibration.
• Every five minutes the cylinder moves. So, from time to time, the pump is not used
• I take data on a pipe and motor and pump. but motor and pumps are normal. My post is about piping vibration
• Pump type  is Piston.
• Our main issue is "abnormal Noise and sound"
• The dominant frequency is Motor RPM

According to the your comments I will do this And I will tell you the result:

1. Test the leakage
2. By the "BUMP TEST", I will calculate the "Natural frequency".
3. Attach a movie and a sound of the problem

Kind regards

Alireza

#### Attachments

Photos (1)
Videos (1)
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You can see the movie about the issue in the attachment.

It has been proved to us that this is not the case when oil is cold,For this reason, the amount of vibration in this movie is not high. But you can see vibration changes between seconds 16 to 23.

1. Resonance (Proven by Bump Test- See attachment)
2. Leakage (Because there is no problem when it's cool)

I advised to increase the number of clamps to increase the stiffness of the system(K), so that Resonance does not occur.
Because, as you can see in the picture, the connection is loose at the exact points.

Thanks again to the attention of all my friends.

If there was an opportunity in the future, I will attach the Time signal after fixing the piping.

If you have a different opinion, I'm hearing.

#### Attachments

Photos (1)
Videos (2)
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Payesh Sanat پایش صنعت کویر posted:

You can see the movie about the issue in the attachment.

It has been proved to us that this is not the case when oil is cold,For this reason, the amount of vibration in this movie is not high. But you can see vibration changes between seconds 16 to 23.

1. Resonance (Proven by Bump Test- See attachment)
2. Leakage (Because there is no problem when it's cool)

I advised to increase the number of clamps to increase the stiffness of the system(K), so that Resonance does not occur.
Because, as you can see in the picture, the connection is loose at the exact points.

Thanks again to the attention of all my friends.

If there was an opportunity in the future, I will attach the Time signal after fixing the piping.

If you have a different opinion, I'm hearing.

I forgot to express the result of the bump test...

Natural Frequency of Piping=25hz

Motor RPM=25hz

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How is that your modulation interval in the movie is very short (around 2 seconds) compared to 39 seconds in your initial twf pictures? Is that also connected with oil temperature or am I missing something?

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Becar posted:

How is that your modulation interval in the movie is very short (around 2 seconds) compared to 39 seconds in your initial twf pictures? Is that also connected with oil temperature or am I missing something?

You do not make mistakes
There is exactly another modulation in the signal.
Look at the attached movie.(I zoomed in on the first signal.)

there is one another modulation interval around 3 sec.

Can this beat be due to the difference between the natural frequency and the motor speed?

20 RPM of difference can make this beat.
(We know that the motor speed is not exactly 1500 RPM.)

#### Attachments

Photos (1)
Videos (1)
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Your shorter time modulation picture is more common for two machines that operate at the same speed or when the machine load is changing over time. This one's amplitudes and  prominence aren't so critical so I wouldn't pay much attention.

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Becar posted:

Your shorter time modulation picture is more common for two machines that operate at the same speed or when the machine load is changing over time. This one's amplitudes and  prominence aren't so critical so I wouldn't pay much attention.

Yes. That's more common

But here we have only one Motor (Other Motors are off)
The only remaining factor to create the beat is The difference between the Motor speed and the natural frequency.

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Payesh Sanat پایش صنعت کویر posted:

Hi Dear All,
In a hydraulic system,an unusual vibration is observed.
The maximum amplitude of the vibration is observed in the pipeline.
The amplitude increases every 40 seconds for 7 seconds.(Picture)
There is only one Electro-Pump in this system and in this building.

What do you think?

please make an bubble chart as shown below to fix the resonance.the below chart is showing only pump and motor but you please include all your piping system.

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