How To Reduce Noise During The Production Process of Rotary Vane Vacuum Pumps

The noise of a rotary vane vacuum pump usually refers to the noise level measured under ultimate vacuum conditions when the pump temperature has stabilized.

It includes the noise from the pump itself and the motor noise.  For users, they are also concerned about the noise during the startup phase before the pump temperature stabilizes, the noise during operation at different inlet pressures, and the noise when operating with the gas ballast open.  Therefore, multiple influencing factors need to be considered.

In terms of the location of the sound source, the pump noise may come from the following aspects:

(1) Impact of the vanes against the cylinder wall, and the sound from pressurized oil in the residual volume and the exhaust dead volume clearance;

(2) Impact of the exhaust valve reed against the valve seat and its support;

(3) Echoes within the oil reservoir and the sound of bubble collapse;

(4) Bearing noise;

(5) Noise caused by large amounts of gas and oil impacting components like the oil baffle;

(6) Others.  Such as noise from the drive system, fan noise in air-cooled pumps, etc.

(7) Motor noise, which is a crucial factor.

Design and treatment recommendations are described below:

1.   Impact of vanes against the cylinder wall.

If the design, manufacturing, or material selection is improper, causing the vanes to slide unsmoothly, or if an exhaust dead volume exists where incompressible oil prevents the vane tip from always closely following the cylinder wall during operation, it will cause the vanes to impact the cylinder wall and generate noise.  Therefore, a structure using an arc-shaped separation between the intake and exhaust ports is recommended.  Use an exhaust flow guide groove to eliminate the dead volume.  When using a linear separation structure, the distance from the end point of the exhaust to the tangent point should be minimized.  For pumps below 70 l/s, considering the actual thickness of the vanes, a distance of 7~10 mm is recommended, with larger values for larger pumps.  If too close, due to the presence of the rotor vane slot and the vane tip having only a narrow contact band, the sealing effect may be compromised when the vane reaches the tangent point position.  This can affect the pump's pumping speed and even its ultimate pressure.  It is evident that this structure cannot completely eliminate the exhaust dead volume, limiting noise reduction levels.

It should be noted that excessive clearance between the vane and its slot will reduce performance.  Therefore, reasonable tolerance fits and geometric tolerances must be ensured.  Consider the thermal expansion of the vanes, avoid scoring between the vanes and slots, pay attention to the cold oil viscosity, and design sufficient vane spring force.  When using an arc-shaped separation, the additional eccentricity of the rotor center should not be too large.  Otherwise, as the vanes pass over the two arcs, they may tend to detach from the cylinder wall at the intersection point, causing impact noise instead.  Generally, 0.20~0.25 mm is sufficient for small pumps;  larger pumps can be appropriately increased.

Sound from pressurized oil in the exhaust dead volume and residual volume.  When the pump reaches ultimate pressure, the pressurized oil in these two locations will be ejected at high speed into the vacuum chamber when connected to it, impacting the rotor and cylinder wall and generating noise.

The size and location of these two volumes relate to the noise level.

2.   Impact noise of the valve reed against the valve seat and support.

Higher gas intake volumes and more circulating oil lead to louder valve noise.  Higher valve lift, larger valve area, and the valve material also affect noise.  Rubber valve reeds should produce less noise than steel or laminated plate ones.  Therefore, oil intake should be controlled, valve closure should be timely and tight.  Pay attention to valve material selection and structure.

3.   Echoes within the oil reservoir and bubble collapse noise.

This noise increases with higher gas loads.  Therefore, this noise becomes noticeably louder when the gas ballast is open or when vented to atmosphere.  If the gas ballast flow is adjustable, it can be reasonably regulated.

4.   Noise generated when large amounts of gas and oil impact components like the oil baffle during discharge.

If components lack sufficient rigidity or are not securely fastened, causing vibration and collision, this noise will increase.  Therefore, the baffle plate should not only have sufficient rigidity and be securely fastened, but also, when contact with other parts (like the oil tank) is necessary, using rubber pads can avoid collision noise caused by vibration and improve the baffling effect.