Manual Vi setting for Howden WRVi255

[desaipt2003]

We are going to replace a Howden MK5/WCV255 with Howden MK6/WRVi. New compressor is supplied by a package supplier saying that the WRVi is direct replacement of WCV. WRVi model consists of a manual Vi setting in the range of 2.2 to 5.0 turning a square headed knob located below shaft on drive side end cover. For 2.2 Vi, the knob has to be rotated clockwise and for 5.0 Vi, it has to be rotated anticlockwise. WCV model don't have such a knob.

My question is what should be the initial setting of Vi when making the test run? What will be final and permanent setting for continuous operation. I am new to this field and don't have much experience for Howden.

[NH3LVR]

I know this should be in SI units, but I have to run off and just have a couple of minutes.
VI=Discharge Pressure (absolute) divided by absolute Suction Pressure. An example is 5lbs suction and 150lbs discharge. Add 14.7lbs to the suction for absolute suction pressure (19.7lbs) Add 14.7 to the discharge (164.7). Divide 164.4 by 19.7=8.3 ideal VI.
You will note that unless your head is quite low or your suction quite high, you may always be under compressing.
Most adjustable VI Compressors are used in two stage systems or medium or high temp applications.
Most screws top out about around 5.0 VI.

[asif]

Please share Howden WRV204-11058 standard CI Oil injected screw compressor service manual

[RANGER1]

If you can give us your suction discharge pressures will pass on corect Vi setting .
I would have thought package supplier should give you the info and manual as part of the deal .

[desaipt2003]

Yes, I got the confirmation from package supplier and OEM of compressor to set it to 5.0

[Josip]

Hi, desaipt2003

please check attachment...

.... resolution is not the best, due to upload limit of 100kb, but ..

Best regards, Josip

[desaipt2003]

Dear all,

We have replaced the compressor and did the pressure test, vacuuming, new refrigerant and oil charging. During the test run we are getting the trouble of high oil temperature. System is tripping on "Oil manifold High-High temperature" after 40-45 minutes of operation. Compressor discharge temperature reaches 115-120 deg. C against 95 deg. C in same system operating in our second plant. What can be the reason of high oil temperature?

[Grizzly]

Because your discharge temperatures are higher.
The oil Temperature is higher!
Is the 2 comps on a common discharge line.
Or if they are separate then there is an issue at the condenser.
Can't advise any further as I don't know your system.
Please advise further.
Grizzly

[RANGER1]

There are several things to point out on the limited info you have posted .

Machine should not be even running with dicharge temp that high .
Maximum is 100 deg C

With WRC compressor it had no oil injection into rotors and it apparently ran ok .
This would indicate a higher than normal oil tempreture affecting discharge temp .

You need to supply the following .
1 .refrigerant or gas being pumped
2 .suction gas inlet temp to compressor
3 .oil pressure above discharge pressure
4 . description of oil circuit and process you are doing
5 . Pressures you are operating at ie suction and discharge pressures .

[desaipt2003]

Dear Ranger1,

1 .refrigerant or gas being pumped - R134a
2 .suction gas inlet temp to compressor - varying
3 .oil pressure above discharge pressure - 2to 3 kg/cm2
4 . description of oil circuit and process you are doing-
5 . Pressures you are operating at ie suction and discharge pressures - Suction : varying from 2.5 kg/cm2 at initial start up to 0.15 kg/cm2 at tripping time./ Discharge : 8 to 8.5 kg/cm2.

The compressor is loading up upto 40% during first 5 minutes of operation and getting down agian to minimum (12-13%) within 3 minutes of capacity. \system trips on oil manifold temperature high-high.

When consulted the vendor, they are telling that the system is short of refrigerant and it has to be charged with additional refrigerant in few steps and to watch the performance after each addition. Is shortage of refrigerant can be the potential reason from oil temperature hike?

[RANGER1]

What is complete serial number of machine ? We require rotor lenth .

Also what type of oil cooler and how is it cooled ?

[Magoo]

You have to regulate the slide injection oil port to control discharge temp.

[desaipt2003]

Dear Ranger1,

Serial No. of machine is MK6B/WRVi255130/667.

Oil cooler is shell and tube type heat exchanger with oil on shell side and cooling water on tube side. Oil flow through coller is controlled by a TCV(Temperature control valve). But I think that is not the matter of concern. We are getting high discharge temperature at compressor. As per vendor, due to shortage of refrigerant, it is getting superheated in evaporator which is causing the trouble of high discharge temperature and in turn high oil temperature.

[RANGER1]

Do you have reason to think that you are short of refrigerant ?

What is oil temp , as i think its still important that this is working satisfactorarily ?

To me not knowing what you are cooling , it seems odd that compressor can load up and achieve set point and unload in very short time .
Maybe things are short of refrigerant as only this and oil cooling could cause these tempretures .
Is oil cooler running to its max capacity
with control valve fuuly open ?
It should probably be cleaned out anyway .

I would have thought discharge temp should be below 60 deg C with 10 deg C s/heat and 80 deg C with 30 deg C s/heat .

There is no oil injection to cool discharge gas so its more than likely s/heat due to low refrigerant charge and/or oil cooler not working as well .