How to detect a compressor reverse during power interruption

Yes it is called a reverse rotation monitor. Bently Nevada makes one.

Thks, appreciated. I went to do a search on that. But need to attach 2 promixity probes.

Is there any ways know beside this method?

Say from the current etc. (Curious)

<Say from the current etc. (Curious) >

By definition, there won't be any current during a power interruption.

Ya understood, what i meant is that if the compressor run reverse, is there symptons we can observe except by attaching 2 proximity probes to detect the reverse as mentioned in the 1st reply.

Thank You.

Loss of pressure or lack of would be one

It's preventable by fitting a non-return valve downstream of the compressor.

Yes. Most industrial screw compressors will have a pressure check valve to prevent the pressure in the separator tank from pushing oil back into the compressor and "burping" this oil into the compressor room. If you have to worry about reverse rotation, you also have to worry about flash fires in the system.

We are building electric motors with a mechanical anti reversal clutch. These motors can only run in one direction. Even if no electrical power is connected, the motor shaft can only be turned in one direction.

An other solution is a motor with a brake.

I've heard about it, never actually seen it although I have seen several compressors come to a sudden halt before (that is always bad). How does the detector work? Can somebody link it?

The detector is like a phase detector,

where P1 is say 90 Deg ahead of the 2nd... so

____|-------|_____

________|------|______

Now if the 2nd leading edge arrives 1st, then the direction of rotation is reverse (look at the pulse forms from the right to left, ie. reverse)

Reciprocating compressors usually have one way reed valve in each cylinder head to prevent backflow of the high pressure output back into the cylinder.

Other types can be protected by use of check valves in the output or discharge line.

One installation had a steam turbine that ran the compressor in event of power outage to maintain air output pressure !

I agree with all the caveats concerning not exposing the compressor to run back,I had a rootes blower runback so fast it wrecked the motor.Didn't do the blower much good either.

However on the topic of detecting motors rotating when not powered,there are commercial systems available which monitor the presence of small voltages, detectable at the motor terminals,generated by the interaction of rotor remanence with stator windings when the motor continues to rotate in ether direction,using the ordinary wiring without additional sensors.

These systems are intended to ensure motor standstill before reversal,or brake or locking pin engagement,and cannot normally detect direction,but only continued rotation.I suppose that the phase sequence of the small voltages could be detected and give direction,but I dont think any commercial device does this.Anyone want a go and patent it?Royalties to my favourite charity.

The concern in relation to centrifugal compressors is if the machine shuts down, and if the discharge check valve leaks, that the discharge pressure flows back into the machine and spins it up in a reverse direction.

This has two main negative consequences, The first is that some gets hurt maintaining the machine because they do not know it is turning, and the second is that many dry gas seal designs are unidirectional, and if you spin them backwards it will tear them up.

Here is the reverse rotation monitor

http://www.gepower.com/prod_serv/products/oc/en/downloads/3300_52reverse.pdf

It is also possible to look at the shaft orbit and based on the direction of precession know that it is reverse, but often times the best indication is that the machine is vibrating as if it is running when it is supposed to be stopped, because it is indeed running...

Thank for all the kind answers, it had been fruitful. :)