hoffman blower intermittent vibration

hello experts, I have a case of vibration in a blower that during certain hours during the day increases the vibration to double and the remaining hours decrease again. I have seen that it has a direct relationship with the opening of the intake valve of the blower. Please I need your advice to understand this dynamic behavior.

I have attached the file.

If you need more information do not hesitate to ask please.
Ill appreciate your comments.
Thank you.

Attachments

Original Post

As u know all blowers have a performance design curve .u can find best efficiency point by setting its flow and dynanic head or out put pressure . When u close input when the output open high diffrential pressure occurs.this state couse high axial movment and so high vibration.you shoud keep the upstream and downstream pressure according to design spec of blower

Thank you for your reply John. See atached.

The system has 5 lamson series 1600 blowers that aerate a wastewater treatment tank. Normally 4 of them work to give an air flow of approximately 45 m3 / h. Automatically the suction valves are regulated according to necesity.

  The blower "D" when the ambient temperature increases, the air density decreases, automatically opens from 40 to 55 percent, normally from 2-7 pm and the amplitudes increase.

Also atached performance design curve(for AZIZ58)

Coincidently the D and the B does not have the impulse manometers to see the diferential pressure as AZIZ58 comment. The pressures of the others go around the 1.05 Bar around 15,2  psi. 

When installing the gauge, I will see how the impulse pressure behaves in the hours of greatest amplitude of vibration.

I will send to clean the suction filter although it looks something clean.

Is it OK to regulate with the intake valve?

Ill appreciate your replyes.

Thank you.

Attachments

I observed the same behavior on similar equipment in the past. The cause was the opening of the valve loaded the motor and caused it to slow down by 5 RPM. The slight speed change made the blower running speed excite a frame resonance. Can you do impact testing or start-up/run down data to confirm the frame/system natural frequencies?

Thank you Bill for your comments. Ill put a reflective tape in the blower shaft to see exactly the shaft speed.

Next week, we are going to stop the blower to see the hot alignment and  I will take to make the measurements (coast down and impact test).

Thank you very much!!

Nestor Lopez posted:

Thank you for your reply John. See atached.

The system has 5 lamson series 1600 blowers that aerate a wastewater treatment tank. Normally 4 of them work to give an air flow of approximately 45 m3 / h. Automatically the suction valves are regulated according to necesity.

  The blower "D" when the ambient temperature increases, the air density decreases, automatically opens from 40 to 55 percent, normally from 2-7 pm and the amplitudes increase.

Also atached performance design curve(for AZIZ58)

Coincidently the D and the B does not have the impulse manometers to see the diferential pressure as AZIZ58 comment. The pressures of the others go around the 1.05 Bar around 15,2  psi. 

When installing the gauge, I will see how the impulse pressure behaves in the hours of greatest amplitude of vibration.

I will send to clean the suction filter although it looks something clean.

Is it OK to regulate with the intake valve?

Ill appreciate your replyes.

Thank you.

 Hi nestor

According to performance curve for type 1600,by decreasing the flow rate presure increas up to 2 bar when D blower start.so differential presure go up and cause to back flow in blower

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