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    Exclamation Ammonia Spiral Freezer Issue



    Dear All,

    I am faced with a challenging issue on an Ammonia plant for a Spiral Freezer. The compressor is a Kobelco Compressor (Screw). I was called upon from the client since they lost the PLC program for the entire system - Once the program was back online (the original one from Frigo-technica who basically supplied the skid) we started the compressor which worked fine till it stopped pulling down the temperature somewhere at -20C (around 1.6 bar).

    Being 100% loaded; the system keeps struggling to pull the load down but doesn't manage it.

    The ammonia Pump is off for supplying to the spiral, I tried closing the liquid inlet to see if there is too much vapor ingress instead of liquid; I manually shut down the startup bypass valve and also played with the oil return from the oil separator but nothing helped.

    The condensing pressure stays at 12.5~13.5 bar with liquid injection oil cooling.

    Any ideas pointers to diagnose this one would be highly appreciated!less



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    Re: Ammonia Spiral Freezer Issue

    Yaris,
    Can you check calibration of slide valve, as it may not be calibrated in new programme.
    There may be some way of forcing it with solenoids or relays etc.
    You may have to check all setpoints as well (If programme will let you).
    Ammonia pump may cycle off if suction pressure to high.
    Do you see it start & stop at any stage.
    Can you see ammonia level in vessel for pumps?
    Maybe also check economizer operation as well, pressures, temps, cold liquid out to liquid feed re circulator vessel.

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    Re: Ammonia Spiral Freezer Issue

    Some systems discharge pressure also restricts loading is screw as well, probably 14bar

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    Re: Ammonia Spiral Freezer Issue

    Hi Haris
    Does your ammonia pump have a pressure differential switch fitted?
    Have you a dual (or two) gauge to note the pressure diff across the pump?
    Have you tried running the pump in hand?
    Just maybe the system suction has a ramp down limit or some means to smooth our the compressor load?

    Are you running your fans in the room?
    If you are turn them off and try pulling down the temp further first.
    You could have a software setting within the program that is locking the pump out and or suction limiting.
    Also why is the condensing pressure so high for such small load?
    That may be a stupid question given your ambient temps, but over here I would want to check out the Condenser operation.
    Good luck Grizzly.

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    Re: Ammonia Spiral Freezer Issue

    Dear Ranger1,

    Thanks for your reply and help!

    The compressor is at 100% load as the slide valve indicator shows on the compressor itself and is also confirmed by the motor nearing its current limit 400 / 423 amps (250KW motor).

    The ammonia pump is inhibited to run unless the LT Vessel liquid does not drop to -40C.

    The ammonia level seems to be low in the system - I charged 12 cylinders of 30KG each; but doesn't seem to be going anywhere..

    Can you give details on how to check economizer operation; I know that it does actuate at 75% and there is intermittent cooling but my High pressure liquid line does not lose a lot of temperature; from 36C to maybe 32C.

    Quote Originally Posted by RANGER1 View Post
    Yaris,
    Can you check calibration of slide valve, as it may not be calibrated in new programme.
    There may be some way of forcing it with solenoids or relays etc.
    You may have to check all setpoints as well (If programme will let you).
    Ammonia pump may cycle off if suction pressure to high.
    Do you see it start & stop at any stage.
    Can you see ammonia level in vessel for pumps?
    Maybe also check economizer operation as well, pressures, temps, cold liquid out to liquid feed re circulator vessel.

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    Re: Ammonia Spiral Freezer Issue

    Hi Grizzly!
    Thanks for your reply; here are a few replies to your questions:

    Does your ammonia pump have a pressure differential switch fitted? No, I do not think it does;

    Have you a dual (or two) gauge to note the pressure diff across the pump? Yes, the gauges are there..

    Have you tried running the pump in hand? I haven't tried running the pumps manually, since I never got to the Low temperature required to run them. I believe running the pumps will only add more load to the system.

    Just maybe the system suction has a ramp down limit or some means to smooth our the compressor load?

    Are you running your fans in the room? It is just a spiral freezer. no chiller or cold store with air coolers.

    If you are turn them off and try pulling down the temp further first.

    You could have a software setting within the program that is locking the pump out and or suction limiting.
    Also why is the condensing pressure so high for such small load? I have tried looking for the compressor software settings; the system used to work fine two months back on the same settings..
    The condensing pressure stays around the same (ambient = 40C)


    That may be a stupid question given your ambient temps, but over here I would want to check out the Condenser operation.
    Good luck Grizzly.[/QUOTE]

    I will also share other information today as I am just leaving for site; let me know what you guys think.. I will also share all the progress here.. I really hope to solve this one!

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    Re: Ammonia Spiral Freezer Issue

    Hi Grizzly!
    Thanks for your reply; here are a few replies to your questions:

    Does your ammonia pump have a pressure differential switch fitted? No, I do not think it does;

    Have you a dual (or two) gauge to note the pressure diff across the pump? Yes, the gauges are there..

    Have you tried running the pump in hand? I haven't tried running the pumps manually, since I never got to the Low temperature required to run them. I believe running the pumps will only add more load to the system.

    Just maybe the system suction has a ramp down limit or some means to smooth our the compressor load?

    Are you running your fans in the room? It is just a spiral freezer. no chiller or cold store with air coolers.

    If you are turn them off and try pulling down the temp further first.

    You could have a software setting within the program that is locking the pump out and or suction limiting.
    Also why is the condensing pressure so high for such small load? I have tried looking for the compressor software settings; the system used to work fine two months back on the same settings..
    The condensing pressure stays around the same (ambient = 40C)


    That may be a stupid question given your ambient temps, but over here I would want to check out the Condenser operation.
    Good luck Grizzly.[/QUOTE]

    I will also share other information today as I am just leaving for site; let me know what you guys think.. I will also share all the progress here.. I really hope to solve this one!

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    Re: Ammonia Spiral Freezer Issue

    Hi Haris.
    If you are just pulling down the surge drum and your comp is fully loaded.
    Then I suspect that the lp side is being starved. I am intrigued as to what temp you need before the pump runs?
    That is a strange control, if there is no transfer of liquid there is no transfer of load.
    The swept volumes through the comp will reduce with the reduced vapour density as the suction pressure drops.
    Humour me and try running the pump in hand.

    A low suction and sufficient head will cavitate a pump. so look fro a differential.
    Grizzly
    Last edited by Grizzly; 06-07-2015 at 06:05 AM.

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    Re: Ammonia Spiral Freezer Issue

    Possibility of oil accumulation in freezer coil should be checked.

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    Re: Ammonia Spiral Freezer Issue

    Quote Originally Posted by haris View Post
    Dear Ranger1,

    Thanks for your reply and help!

    The compressor is at 100% load as the slide valve indicator shows on the compressor itself and is also confirmed by the motor nearing its current limit 400 / 423 amps (250KW motor).

    The ammonia pump is inhibited to run unless the LT Vessel liquid does not drop to -40C.

    The ammonia level seems to be low in the system - I charged 12 cylinders of 30KG each; but doesn't seem to be going anywhere..

    Can you give details on how to check economizer operation; I know that it does actuate at 75% and there is intermittent cooling but my High pressure liquid line does not lose a lot of temperature; from 36C to maybe 32C.
    Without knowing your plant, but assuming it's a single stage economized compressor.
    The economizer is possibly a seperate vessel which could have the liquid line from high pressure liquid receiver running through it.
    What it does is chill liquid line from liquid receiver before it enters low side accumulator with the ammonia pump, which circulates ammonia through evaporator.
    The economizer vessel usually maintains a level in it to submerge liquid line coil running through it.
    If there is a call to make up level in low side vessel it should be chilled down to below zero, probably a lot more.
    Even if liquid receiver is not calling for liquid it should be chilled if compressor is 100% loaded.
    Possible causes it's not working are no liquid level in economiser, of suction from it going back to compressor side port not opening.
    Without this working big loss in capacity & poor cooling.
    May not be problem, but has to be checked anyway
    Last edited by RANGER1; 06-07-2015 at 12:04 PM.

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    Re: Ammonia Spiral Freezer Issue

    Rangers correct (What's New!)
    Without knowing your plant we are all guessing, what is happening?
    Grizzly

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    Re: Ammonia Spiral Freezer Issue

    Ranger / Grizzly;
    I would post the P&ID here if I could..

    I did try and inform about the system.. Its a single stage system; side port economized.. just like Ranger guessed - The superfeed solenoid valve actuates once the capacity goes over 80% which I guess is OK as far as my little refrigeration knowledge goes..

    There is however an issue of having almost no liquid in the entire system.. the little liquid that there is is probably below the mark of the HP liquid line and suffices only for the liquid injection line for oil cooling..

    I did try and run the pumps as per Grizzly's instruction; Got a +2bar pressure on the discharge side; the issue being almost no liquid (starved LT vessel) I switched them off.

    Last I opened up to check the suction filter which was quite clean. thinking there could be a blocked filter since the pressure transmitter reads just before the filter it might not be reading the actual suction of the compressor.. the oil pressure is ok, the discharge temperature/pressure is ok... no alarms.. the motor does wander on the high side of its current limit (410/423 amps)

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    Re: Ammonia Spiral Freezer Issue

    Sandybapad;

    Thanks for your help and reply.. That too was another issue; All the oil has been drained from the system including the spiral freezer coils..

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    Re: Ammonia Spiral Freezer Issue

    Haris,
    Reading through posts I think I could have been thrown off track when in first post you mentioned closing off liquid in.
    Thinking you were closing high pressure liquid into LT accumulator, but I thing you may have been referring to liquid pump inlet.
    It seems you are basically seriously low on refrigerant.
    Is there any sight glass or probe to check levels in LT accumulator.
    Close high pressure liquid supply off to LT vessel & suction pressure hopefully should dive.
    You will have to look for ammonia leak, suggest condenser could be first port of call, then if positive pressure it might appear elsewhere.
    Alternatively if no leak found could be relief valve has gone off at some stage, maybe you have some other idea, are there any other heat exchangers on this system?
    High pressure trip should be set below relief valves on high side, usually 10-15% below their set pressure.
    Other possibilities could be if compressor has internal relief between discharge to suction short circuiting gas flow.
    Does this system have auto air purger of some kind.

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    Re: Ammonia Spiral Freezer Issue

    it would seem all problems started with down load of new PLC program. it would have been a generic program that would have to be tuned for your application.
    Rapid loading on start up/ first start will generate high agitation in surge vessel, and cavitate the ammonia pump. there will be a differential switch somewhere locking out pump starting.
    Just guessing though. I have some experience with Frigo spirals.

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    Re: Ammonia Spiral Freezer Issue

    haris, is Ammonia gas charged by you is pure? There is possibility of moisture in it. Because if moisture is present in Ammonia, then the suction pressure would go down.

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    Re: Ammonia Spiral Freezer Issue

    Quote Originally Posted by RANGER1 View Post
    Haris,
    Reading through posts I think I could have been thrown off track when in first post you mentioned closing off liquid in.
    Thinking you were closing high pressure liquid into LT accumulator, but I thing you may have been referring to liquid pump inlet.
    It seems you are basically seriously low on refrigerant.
    Is there any sight glass or probe to check levels in LT accumulator.
    Close high pressure liquid supply off to LT vessel & suction pressure hopefully should dive.
    You will have to look for ammonia leak, suggest condenser could be first port of call, then if positive pressure it might appear elsewhere.
    Alternatively if no leak found could be relief valve has gone off at some stage, maybe you have some other idea, are there any other heat exchangers on this system?
    High pressure trip should be set below relief valves on high side, usually 10-15% below their set pressure.
    Other possibilities could be if compressor has internal relief between discharge to suction short circuiting gas flow.
    Does this system have auto air purger of some kind.
    I had my reply all ready after reading a few posts, but Ranger1 beat me to it

    I just want to add one thing, I don't know the Kobelco screw compressor package, from their webpage the design looks pretty basic, and there doesn't seem to be an internal relief valve.

    A compressor package of this size would have a relief valve between the discharge and suction side, both to assist with unloaded start and to equalize discharge and suction when stopping, to prevent the compressor from filling up with oil or rotating the wrong way because of gas blow back through the rotors.

    I would look for a pipe around 1/2 - 1" with a solenoid on it that goes from the oil separator back to the suction pipe of the compressor. the solenoid is most likely a normally open solenoid that should energize 5-10 seconds after the compressor starts.
    if the solenoid is not in the basic PLC program, then this valve is open all the time and shorts out the compressor <--- this might be noticeable by a slightly elevated discharge temp, if you know what the normal temp was, probably around 60-65 celsius.

    it's either this, or as Ranger1 said, close the HP liquid injection to the LP drum and see what happens <- I would do this first.
    -Cheers-

    Tycho

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    Re: Ammonia Spiral Freezer Issue

    Hi all,

    No joy fixing the issue yet..!

    Ranger1 --

    I tried looking for a leak as I too was wondering where'd all the ammonia go!! I couldn't find any so suspecting that one of the relief valves did go off during some point - just trying to figure out which one / which ever one was it; isn't leaking anymore. The plant was off for a while and the city had an ugly spell of heat where it is quite possible that pressures might have gone up to make the valve blow off..

    As for closing the Liquid feed to LT - well I tried doing this initially, When the compressor couldn't pull down the suction I too suspected vapour ingress from Receiver to LT vessel - so I closed the LT liquid feed line as well as any other bypass lines. I also shut off the wet return and the lines feeding the ammonia liquid pumps suction.. ran the compressor for a few hours but it did not budge from 1.8bar.. what confuses me is it works fine from +6 / 7 bar to 2.0 / 1.8 bar like a charm.. and then it struggles as if it was undersized for the same load.. I even tried closing the suction valve to some extent but was scared id damage the machine pulling it down to vacuum too quickly..

    Tycho--->

    Thanks for your help and reply...! You're right about the by-pass I checked the bypass line initially using a temperature gun and then later I manually closed it during operation.. nothing happened.. the valve isn't leaking..

    Do you think it could be the adjustment on the Vi? the compressor is 100% loaded if the Vi is set at =5; if the Vi is set less than 5.. say 3.65 or 2.2 etc; in that case the compressor is not fully loaded.. however loading it further will require more motor power which isn't available.. (just speculating) what are your thoughts / comments on this?

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    Re: Ammonia Spiral Freezer Issue

    Magoo, the program is the same that was running before.. jusst uploaded again the pumps run if i change the scaling setting on the TT to fool the PLC to think its -41C..

    Sandy, Moisture in the ammonia might be a possibility - but then again isolating a vessel and pulling it down with a large compressor should still bring it towards vacuum.. what do you think?

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    Re: Ammonia Spiral Freezer Issue

    Hi, haris

    Quote Originally Posted by haris View Post
    Dear All,

    I am faced with a challenging issue on an Ammonia plant for a Spiral Freezer. The compressor is a Kobelco Compressor (Screw). I was called upon from the client since they lost the PLC program for the entire system - Once the program was back online (the original one from Frigo-technica who basically supplied the skid) we started the compressor which worked fine till it stopped pulling down the temperature somewhere at -20C (around 1.6 bar).

    Being 100% loaded; the system keeps struggling to pull the load down but doesn't manage it.

    The ammonia Pump is off for supplying to the spiral, I tried closing the liquid inlet to see if there is too much vapor ingress instead of liquid; I manually shut down the startup bypass valve and also played with the oil return from the oil separator but nothing helped.

    The condensing pressure stays at 12.5~13.5 bar with liquid injection oil cooling.

    Any ideas pointers to diagnose this one would be highly appreciated!less

    Knowing almost nothing about that system ... speaking all about without any scheme is just guessing ...so I do the same ...

    first are you sure that system was working properly before shutdown and standstill for a while

    and second you must be sure that you have enough liquid in your system otherwise if you charge your freezer with gas refrigerant you cannot go further to reduce suction pressure i.e. temperature ... all is useless if system is starving ...

    Quote Originally Posted by haris View Post
    There is however an issue of having almost no liquid in the entire system.. the little liquid that there is is probably below the mark of the HP liquid line and suffices only for the liquid injection line for oil cooling..

    I did try and run the pumps as per Grizzly's instruction; Got a +2bar pressure on the discharge side; the issue being almost no liquid (starved LT vessel) I switched them off.
    Quote Originally Posted by haris View Post
    The ammonia level seems to be low in the system - I charged 12 cylinders of 30KG each; but doesn't seem to be going anywhere..
    If you have some vessels there ... 360kg of ammonia for sure is not enough .... do you have any level sight glass or level indicator I believe You must charge some more ammonia into system --- there must be some label how much refrigerant is needed for normal operation but you can calculate it by yourself .... approximately ... you have volume of vessels and pipes and you can approximate minimal refrigerant charge ...

    Best regards, Josip

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    Re: Ammonia Spiral Freezer Issue

    Haris can you instal pressure gauge to verify suction & discharge pressures.
    Transducers might be reading incorrect.
    Vi should be set at 5 for single stage, economized.

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    Re: Ammonia Spiral Freezer Issue

    Hi all,

    The issue is still there - checked the sensors and everything. The supplier (FTI) suggests that the compressor block is damaged.

    I am not sure how that holds true, considering the compressors pulls down suction for eg: from 8bar to 3bar in minutes, then from there on it struggles and stops somewhere around 2bar... (absolute)

    If it was damaged, the behavior should have been consistent? or could it be true that it actually is damaged?

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    Re: Ammonia Spiral Freezer Issue

    haris,
    big call.
    The first thing to do is check all oil filters for metal & debris, shiny particles.
    It does happen but not very often.
    Other things like shaft seal might leak, noisier than normal.
    You could also see if drive shaft moves in or out using dial indicator, on Kobelco could be up to 0.12mm,
    if its like a 19LNB or similar.

    How did you check pressure transducers, did you remove them & read atmospheric pressure?
    Or compare with a good pressure gauge?

    Also are amp readings correct, verify with tong tester (amp meter).

    You could also close suction while running to see if compressor will trip on low pressure or good vacuum.

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    Re: Ammonia Spiral Freezer Issue

    Hi,

    I did check the filters and strainers - almost serviced the entire plant including the liquid supply and return lines..

    Tried slowly closing the suction valve, when the valve is near being completely closed, you do hear a heavier sound and well the suction never drops - it did go up slightly (2 bar).

    I swapped sensors, also checked by placing gauges.

    The customers been a bit tricky, initially called me in for an automation task saying they accidentally lost the PLC program and prior to that the compressor was running 100% ok, later I learn't from the operators that the machine had starting losing performance 8 weeks prior to losing the PLC program. My guess is they attempted to fix it locally and in doing so - lost the PLC program parameters only, since the program was there..

    Once I put the parameters back in [the original ones from FTI] - I was faced with this problem..

    To top it off I never got paid for all the services like clearing oil in the lines, servicing the strainers, putting the valves in correct position etc etc.. FTI suggested that the compressor blocks screw set might be damaged.. pfff.. for a machine that had run for hardly 10,000 hrs.. its a pity!

    So I've detached my self from the job.. I'll let FTI (Frigo Technica International) handle the customer! and write off 12 days, air tickets and all other expenses as a loss

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    Re: Ammonia Spiral Freezer Issue

    Quote Originally Posted by haris View Post
    Hi,

    I did check the filters and strainers - almost serviced the entire plant including the liquid supply and return lines..

    Tried slowly closing the suction valve, when the valve is near being completely closed, you do hear a heavier sound and well the suction never drops - it did go up slightly (2 bar).

    I swapped sensors, also checked by placing gauges.

    The customers been a bit tricky, initially called me in for an automation task saying they accidentally lost the PLC program and prior to that the compressor was running 100% ok, later I learn't from the operators that the machine had starting losing performance 8 weeks prior to losing the PLC program. My guess is they attempted to fix it locally and in doing so - lost the PLC program parameters only, since the program was there..

    Once I put the parameters back in [the original ones from FTI] - I was faced with this problem..

    To top it off I never got paid for all the services like clearing oil in the lines, servicing the strainers, putting the valves in correct position etc etc.. FTI suggested that the compressor blocks screw set might be damaged.. pfff.. for a machine that had run for hardly 10,000 hrs.. its a pity!

    So I've detached my self from the job.. I'll let FTI (Frigo Technica International) handle the customer! and write off 12 days, air tickets and all other expenses as a loss
    Sad to hear after your efforts, you get customers now & then like that unfortunately.
    Kobelco screw, can't imagine they will be off the shelf.

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    Re: Ammonia Spiral Freezer Issue

    Quote Originally Posted by haris View Post
    Hi,

    I did .....

    ..... So I've detached my self from the job.. I'll let FTI (Frigo Technica International) handle the customer! and write off 12 days, air tickets and all other expenses as a loss


    Very sad, your client is not good ... at least it will be OK to reimburse your air tickets and accommodation expenses.

    Job you did is not finished (they asked you to came for some other reason knowing they are in some kind of trouble) and about that we can discuss to the end of the world ... hope that will not ruin your soul. Things like that happens sometimes.

    It happened something similar to me 25 years ago - I completed job and compressor was running fine many years after, but payment never arrived (the worst in that episode - client was my very good friend) ... there is no rules how to check our clients ... but I learned something ... travel expenses and accommodation are on client's expenses or I will not come ... sounds rude, but believe me it is not.

    Best regards, Josip

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