Pressure Transmitter

Posted in: , on 13. Apr. 2015 - 14:53

Dear Sir,

We need to control the blower speed centralised vacuum system based on the number of openings at a time by pressure transmitter. Each opening has a pressure transmitter, if I open one point the blower will be in initial speed, If I open the second point the speed should be increased by vacuum.

(we need to control the speed by giving signals from pressure transmitter to PLC and VFD)

Is this possible?

Please give me some relevant ideas for this process.

Best Regards,


Re: Pressure Transmitter

Posted on 13. Apr. 2015 - 03:43



If the pressure transmitter at each opening can monitor, whether the related valve is open or not in a decisive way, a pressure transmitter can be used.

In this case, the pressure at the transmitter location is either atmospheric or at a certain vacuum, depending on the position of the related valve.

If the pressure can range from atmospheric to vacuum, regardless of the valve position, then the pressure transmitter is useless.

A better solution is then to use a limit switch on each valve.


When you are using a PD blower, keep in mind that the allowable vacuum and rpm range is limited.

At higher vacuums, the outlet temperature increases, limiting the maximum allowable vacuum to approx. 500 mbar for a normal PD blower.

A PD blower with pre inlets can go up to approx. 750 mbar vacuum.

At lower rpms, a PD blower suffers from higher internal leakage, increasing the outlet temperature, causing the maximum allowable vacuum at lower rpms to decrease.

When using a centrifugal fan as a central vacuum pump, the air flow is influenced by the vacuum.

That requires at least to use the fan curve as an input for the VFD control.


Another way is to generate a constant vacuum in a central vacuum vessel, connected to all the vacuum points by a piping system with valves.

Such a system uses an oil filled screw compressor, which is fully automatic and installed as “plug and play”.

It requires no local sensors at all.