explain the procedure please.
Here is the answer I gave to another question on centrifugal pump startup. The only difference with a canned pump is the fact that they tend to be much easier to prime due to their geometry.
Assuming the pump is properly primed, The main considerations in starting up a centrifugal pump is the suction and discharge systems, the presence or absence of a check valve in the discharge and its condition as well as the pressure capability of the two systems.
A pump may be pumping against no discharge pressure or it may be pumping against an existing pressure. In the case of no pressure, you need to have the discharge valve closed otherwise you may overload the driver.
If there is existing pressure in the discharge line, there is no concern with over loading either the pump or driver on start up since the pump develops no load until it starts to rotate and build head. If there is a check valve in the discharge and the block valve is open, there is essentially no flow (and therefore no load) until the head developed exceeds the pressure in the discharge line.
The real consideration is having back flow from the discharge to the suction. That is the reason for a properly selected check valve that is properly maintained so it will function as designed. In the case of high pressure pumps where the discharge pressure can exceed the suction pressure to the extent that the suction system could fail it is very important that either the pump be started with the discharge closed or with a properly operating check valve.
One should note that if the pump is multistage, there may be a minimum flow requirement that needs to be worked into the start up procedure to assure there is minimum flow established as soon as possible.
I would assume the only consideration in starting a vacuum pump is the question of maintaining an existing vacuum. In that case you would need as a minimum a check valve in the line to prevent back flow and the loss of the vacuum. Otherwise starting should be similar to starting a centrifugal pump. The final consideration being concern for not overloading the driver on initial startup.