Patent Application
20250198406
The field of the disclosure relates to vacuum pump start up and in certain preferred implementations to reducing torque during pump start up.
A first aspect rotary vane vacuum pump for evacuating a vacuum chamber, said rotary vane vacuum pump comprising: an inlet for connection to said vacuum chamber and an outlet for exhausting fluid pumped by said vacuum pump; a rotor comprising a plurality of vanes and a stator, said rotor being configured for rotation within said stator, said rotor and stator defining a plurality of pumping chambers for pumping a fluid from said inlet to said outlet on rotation said rotor; a motor for driving said rotor; and a venting channel for providing fluid communication between an exterior of said vacuum pump and a pumping chamber within said vacuum pump, said venting channel comprising a flow control device for controlling flow through said venting channel; said flow control device being configured to allow flow through said venting channel at start up of said pump and to impede flow through said venting channel in response to at least one of: a predetermined time elapsing, a speed of rotation of said rotor reaching a predetermined threshold value, a motor current reaching a predetermined value and an output from at least one sensor, said output from said at least one sensor being indicative of operation of said vacuum pump.
When a vacuum pump starts up, it may initially be pumping gas at a higher pressure, for example at atmospheric pressure, and this may involve much larger amounts of torque than during steady state operation when the pressure is much lower. This is due to the additional fluid transferred in the pump that can create a huge resistance in addition to the resistance due to the inertia of the rotor and static friction.
In some types of pump such as a sliding vane rotary oil vacuum pump this is a particular problem as in addition to the gas transfer there is also transportation of the oil used for sealing the vanes at start up. The torque to overcome these forces at start up creates an initial loading on the pump motor that may be several times higher than the loading during normal steady state operation. This may be the limiting factor when determining the size of motor to drive the pump. It may also lead to a potential start up failure during the lifetime of the pump.
It would be desirable to be able to reduce the torque during start up.
The inventors recognised that the torque to rotate the rotor of a vacuum pump at start up, particularly one that pumps down from atmospheric pressure can be very large and is often the limiting factor when selecting a motor to drive the pump. They also recognised that much of the torque was due to the pressure difference across the vanes during initial rotation and that this could be alleviated by providing controlled venting of the pump at start up such that fluid is able to enter the inlet pumping chamber. After a certain point then flow through the venting channel may be impeded or stopped and the vacuum pump can function in the usual way. By reducing the pressure difference across the vanes using a venting channel that provides a fluid passage to a region that is not at a reduced pressure, the maximum torque during startup is reduced. The venting channel may vent to atmosphere or in some cases to an increased pressure region such as an oil casing.
Selecting the point at which it is most preferred to stop venting may be done based on one or more of a number of different factors that are indicative of the operation of the pump. It may simply be a certain time after start up. Alternatively, the decision to stop venting may be based on the operation of the pump itself, so it may be based on one or more of a speed of rotation of the rotor reaching a predetermined threshold value, a motor current reaching a predetermined value or an output from a sensor indicative of some operational parameter of the vacuum pump. Basing the decision on the detected operation of the pump may allow the venting to be stopped at a preferred or optimal point. The sensor may be a sensor associated with the vacuum pump or it may be associated with the system that the pump is pumping.
In some examples, said vacuum pump comprises said at least one sensor.
In some examples, said at least one sensor comprises at least one of a temperature sensor, a pressure sensor, a humidity sensor, and a sensor for sensing a number of rotations of said rotor.
All of pressure, temperature, humidity and number of rotations since start up of the rotor are relevant to the current state of the vacuum pump and one or more these measured values may be used in the decision to stop venting the pump.
In some examples, said inlet comprises a movable closure element for opening or closing said inlet, said movable closure element being configured to move between an open and a closed position in response to a pressure on a vacuum pump side of said movable closure element rising above a pressure on a vacuum chamber side of said movable closure element; wherein said venting channel is in fluid communication with said vacuum chamber side of said movable element, such that said fluid control device allowing flow through said venting channel causes said movable element to move to said closed position.
Vacuum pumps may have moveable closure elements for sealing their inlets such that the vacuum chamber to which they are attached can be sealed in a vacuum state when the pump is turned off. In some cases these moveable closure elements are moved to a closed position under control of a flow control device that may be opened to allow flow through a channel, the flow changing the pressure on one side of the movable closure element, such that opening the channel changes the pressure difference across the closure element pushes it to a closed position. The flow control device may conventionally have been a solenoid valve controlled by power sent to the motor, such that on stopping the motor the valve is opened and the closure element closes, while on starting the motor it is closed. In examples, the system for controlling the movable closure element may be combined with a system for venting the pump at start up. Where this is the case, then this can reduce the number of flow control element involved, with one flow control element, which in some cases may be a valve, being used for both controlling the moveable closure element and for venting the pump on start up. In this case rather than closing the valve immediately when starting the motor, the closure of the valve is delayed such that during the initial stage of rotation of the pump there is venting of a pumping chamber and the movable closure element remains closed.
In some examples, the venting channel is configured to open into the rotary vane pump closer to the inlet of the vacuum pump than to the outlet.
The venting channel may open into the pump close to the pump inlet which is where the gas suction occurs. In some examples it may open into the vacuum pump downstream in the direction of rotation of the pump from the inlet such that the venting channel opens into the inlet pumping chamber.
In some examples, said venting channel provides venting to an exterior of said vacuum pump at atmospheric pressure.
In other examples, said venting channel provides venting to a pressure above atmospheric pressure.
In some examples, said rotary vane vacuum pump comprises a lubricant sealed sliding vane vacuum pump and said venting channel provides venting to a lubricant casing of said pump.
Where the vacuum pump is a lubricant sealed vacuum pump, then it may be advantageous to vent to the lubricant casing as this avoids lubricant contamination from the venting channel that may be a problem when the pump is stopped such as during transportation.
The venting chamber provides venting by providing fluid communication between the interior of the pump and the exterior of the pump or the lubricant casing. The venting channel may open at one end into a pumping chamber and at the other end somewhere exterior to the vacuum pump or within the lubricant casing of the vacuum pump.
In some examples, said flow control device is configured to open said venting channel or close said venting channel.
In other examples, said flow control device is configured to control a degree of opening and thus, a flow through said venting channel.
Although, the flow control may be done in a number of ways, in some examples the flow control device comprises a valve.
In some examples, said valve comprises a mechanical valve comprising a resilient member for biasing said closure element towards said closed position.
In other examples, said valve comprises an electrically controlled valve configured to operate in response to control signals sent by control circuitry.
Where the valve is an electrically controlled valve then there may be control circuitry to control the valve. Such control circuitry may add slightly to the complexity of the vacuum pump, however it may also allow the start up phase to be more carefully controlled and provide a very effective reduction in the maximum torque.
In some examples, said rotary vane pump further comprises control circuitry configured to control said motor for driving said pump; and to control said flow control device; said control circuitry being configured to control said flow control device to allow flow through said venting channel at start up of said pump, to control said motor to start driving said pump and then to control said flow control device to impede flow through said venting channel.
Although, the control circuitry may simply control the valve to open after a predetermined time, in some cases it may be more sophisticated in its control and may respond to signals from one or more sensors when determining the preferred or optimum time for impeding the flow through the venting channel. In some cases the control circuitry may comprise an algorithm for determining when to stop venting based on a plurality of inputs.
A second aspect provides a method of starting a rotary vane vacuum pump according to a first aspect, said method comprising: controlling a flow control device to allow flow through a venting channel; starting rotation of the rotor of the pump; and in response to at least one of a predetermined time elapsing, a speed of rotation of said rotor reaching a predetermined threshold value, a motor current reaching a predetermined value and an output from a sensor, said output from said sensor being indicative of operation of said vacuum pump, impeding flow though said venting channel.
In some examples, said method further comprises: causing a movable element to move from obscuring an inlet to said vacuum pump to open said inlet to said vacuum pump by said step of impeding flow through said venting channel.
In some examples, said step of impeding flow through said venting channel comprises closing a valve.
Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.
Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.
Examples of the present disclosure will now be described further, with reference to the accompanying drawings, in which:
Before discussing the examples in any more detail, first an overview will be provided.
At start up of a vacuum pump and in particular a sliding vane oil sealed vacuum pump there is a high load on the motor due to inertia, pressure differences across the vanes of the pump and transportation of the oil. Examples seek to reduce the load experienced at start up by venting the pump so that pressure difference across the vanes of the pump are reduced by fluid flowing into the inlet the pumping chamber through the venting channel. This venting can be done by opening a valve in a flow path between the pumping chamber and the exterior of the stator.
The valve may be a mechanical valve that operates in response to a difference in pressure or it may be an electrical valve, driven by electronic control circuitry. The valve could be a modulated valve or a binary valve with an ON/OFF state.
The control of the valve may be synchronised with the operation of the pump at start up for example with the pump rotation speed and/or a time period.
For an oil sealed pump, the venting of the inlet pumping chamber when the pump is stopped and during start up limits suction due to reduced pressure in the pump and thereby the amount of oil that is sucked from the oil casing into the pump. This reduces the amount of oil in the pump at start up and the torque at startup is correspondingly reduced. The duct or channel used for venting may open into the outside or it may be linked to the pump oil casing which is at an increased pressure (atmospheric pressure+overpressure due to the gas extraction).
The valve may be controlled by ON/OFF switch valve, or proportional valve.
The motor power is reduced at startup by the venting and this allows a lower motor size without decreasing pump performance.
Some pumps are configured with a solenoid valve that is used to control a movable closure element or shutter for sealing the pump from the vacuum chamber before stopping the pump. Such a valve controls flow through a passage that is used to increase the pressure on one side of the movable closure element so that it moves to seal the pump from the vacuum chamber. This valve might be a solenoid valve that is controlled by the pump power supply, so that on powering up the pump the valve closes. Examples couple this venting passage and valve to an additional venting channel into a pumping chamber, so that the valve can be used to control closure of the movable closure element and also to vent the pumping chambers to allow the pump to start more easily. In this case rather than closing the valve at power up of the pump, the valve is closed at a certain point during start up of the pump, for example after a predetermined time, or at a predetermined speed whereupon the valve may be closed so that the pumping chambers are no longer vented, and the pressure in the pump reduces and the movable closure element opens.
In summary an integrated control and management of the solenoid valve allows the vent to remain open during the start up phase, for one of a defined period of time; a defined rotor speed being reached or a pressure, temperature, number of rotations of the rotor or humidity being reached and independently of the pump power supply.
In this example there is an oil casing 32 that supplies the oil for the oil sealed pump and the venting channel 7 in this example opens into this oil casing 32. This is at an increased pressure compared to atmospheric pressure. Venting into the oil casing has the advantage that contamination from oil in the venting gas leaking to the exterior of the pump is avoided or at least impeded.
Control circuitry 15 controls the motor and the valve 7 for venting the pump, so that on start up control circuitry controls the motor to start driving the rotor and the valve to remain open. After a predetermined time, and/or on receiving a signal from the sensor 11 indicating a predetermined condition such as a threshold temperature being passed, the control circuitry 15 controls valve 7 to close, whereafter shutter 9 will open and the pump 1 will start to evacuate the vacuum chamber 2.
Where there is a valve for venting the pump (dotted line 60) then the torque at start up is smaller. It should be noted and as shown by this dotted line 60, although the torque initially during start up is significantly reduced it does remain higher for longer as it takes longer to evacuate the chamber and reach a steady low pressure state if the pump is vented initially.
When this condition has been met then the vent is closed at step S30. The pump then continues to pump and evacuate the pumping chamber. Where there is a shutter between the vacuum chamber and vacuum pump, then this shutter will open once the pressure in the pump has fallen to a value lower than the pressure in the vacuum chamber. At step S40 instructions are received to stop and pumping is stopped. At this point the method returns to step S10 where the pump is stopped and the vent is open. In some examples where the pump has a shutter to the pumping chamber then this will close.
Although illustrative examples of the disclosure have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the disclosure is not limited to the precise example and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the disclosure as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22305762.1 | May 2022 | EP | regional |
This application is a national stage entry under 35 U.S.C. § 371 of International Application No. PCT/EP2023/063802, filed May 23, 2023, which claims the benefit of EP Application Serial No. 22305762.1, filed May 23, 2022, the entire contents of each of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/063802 | 5/23/2023 | WO |
