View Full Version : Starting a large screw compressor in fully loaded position?

24-11-2013, 07:35 AM
What would happen if a large screw compressor was started in a fully loaded position?

24-11-2013, 08:32 AM
It would draw a lot of current!
I have seen on very large systems the oil charge get pumped out of the system.

24-11-2013, 09:40 AM
simplygold, come on tell us what happened, we won't tell anyone!

It won't hurt compressor normally but will stretch starter gear as hookster mentions, high current.

Everything should have protection, starter gear etc.

Could possibly damage drive coupling if overloaded.

24-11-2013, 02:19 PM
Hi simplygold.
Yours is an intriguing question!
Because most large compressor systems have a start inhibit, if the slide valve is not below say 3% load position.
Also the internal spring is designed to drive the slide back to unload position, prior to enough internal oil pressure being present to drive the slide open.
As asked already
Out of interest what type / model do you have?
Even if the slide was fully across, I would not expect the pressures initially to be excessive?
A faulty non return valve on the discharge maybe? (Not all have these.)
What has happened to make you ask?
This comp would not have a vsd on it by any chance would it?

27-02-2014, 02:40 AM
The magic smoke comes out of the motor and the china man has to put it back in

03-03-2014, 10:04 PM
Hi, simplygold :)

What would happen if a large screw compressor was started in a fully loaded position?

Did you try to start? ...... What is outcome?

Best regards, Josip :)

04-03-2014, 04:37 AM
Hello Simplegold.
If by chance you mickey mouse the control system in place and started the compressor fully loaded, all hell would destroy the motor control system and at worst apply the national grid to the drive motor. With resultant flash overs and mayhem. NOT recommended.

04-03-2014, 08:41 AM
I have seen some compressors, ex: rtaa trane chiller,due to stuck of the slide valve, it will start, will go to after some time low saturation alarm or high winding temperature. I think it will increase the inrush current and it may give more stress to bearings.

04-03-2014, 10:16 AM
If properly protected, protection devices will cut off. What do you mean with 'happen'? With the electrical motor, the screw, the oil, ...

10-03-2014, 04:50 PM
almost all of screw compressor has unloading start system .
some of them those not start until your system comes to %0
some of them automatically goes to %0 when your system is off
also in good design you have current limits control to protect your motor from over current

22-03-2014, 08:21 AM
The control board thinks that the slide valve is in 0% position when in reality it is fully loaded. The slide valve indicator shows the true position and the amps on the motor are consitent with full load. What happened was that the compressor was turned off and then started up by someone who did not know that the computer thought the compressor was unloaded. This compressor is driven by a 700hp motor, so any damage to the motor is very expensive to repair.

Luckily there isn't any damage to the motor and we manually load and unload the slide valve on the hydraulic stack valve when we take the compressor down.

22-03-2014, 11:30 AM
Maybe elementary solenoids coils are reversed?