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  1. #1
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    Oil Pressure Differential Switches


    The OSP1 Copleland oil pressure switch has a normally closed relay contact which opens if the oil pressure falls too low for too long. This switch does not have a fault signal terminal.

    I believe that there is a version of this switch which has a fault signalling terminal. Does anyone have knowledge of this: a connection diagram: a web site?



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    Re: Oil Pressure Differential Switches

    Danfoss do one with a fault indication signal.

    T1 = neutral
    L = control circuit in
    M = control circuit out
    S = fault signal
    230 = live in (for the heater)

    You can get them with a variety of time delays. i.e. 60 secs, 90 secs or 120 secs.

    The wiring diagram is on the inside of the cover.
    I'm back on the Pale

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    Re: Oil Pressure Differential Switches

    Danfoss designation MP55 or MP54 should do the job, wiring diagrams on the Danfoss web site and has an alarm output.

    Ian

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    Re: Oil Pressure Differential Switches

    What the world needs is an oil pressure switch that will reset itself after about an hour. An hour is more than enough off time to protect the compressor and this could save a lot of products.
    Last edited by Gary; 22-02-2007 at 07:47 AM.

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    Re: Oil Pressure Differential Switches

    Gary
    are the oil fairies going to come in during that hour and change the oil and filter if it is blocked ready for the compressor to start again.

    Ian

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    Re: Oil Pressure Differential Switches

    It won't fix the problem, but it may (or may not) save the products.

    A blocked oil filter is but one in a long list of possible faults.

    The important question is whether this would damage the compressor? Since oil switches allow the compressor to run for 2 minutes with no net oil pressure, presumably this is the longest it can run without damaging the compressor, given sufficient off time to cool the bearings.

    But this could be shortened also. For example, after automatic reset, the trial period could be reduced to 1 minute (if needed). And/or the switch could limit itself to 3 restarts (within a 24 hour period?)... or 2... or 1. Given todays electronic controls, there are any number of possible strategies.
    Last edited by Gary; 22-02-2007 at 03:37 PM.

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    Re: Oil Pressure Differential Switches

    Gary
    are you presuminmg that on auto reset the compressor will pull the product down to temp in the two minutes of running? I have had to do numerous rebuilds due to people resetting oil switches without sorting the fault, and you are suggesting letting the plant commit suicide itself, without human intervention.

    IAn

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    Re: Oil Pressure Differential Switches

    Can i add another train of thought to this list of diatribe. Can we then assume that all safety devices can be palyed with and times for resets altered.Let me give you a for instance , take your car and the brake fluid warning light, can we assume following the train of conversation that we can now have a reset switch placed on our dashboards so when this light shines out on the motorway at 80mph/100kph we can then press this button and hope that in a hour the brake cylinder will have refilled itself and all will be back to normal. Or would you stop and check your fluid manually and top up as needed AFTER finding out where the fluid has gone...........

    I think most people would attend the nearest lay by or garage rather than hope the fault will just go away.

    OR perhaps the LP switches fitted as saftey cut outs can now come with a link cable in the packet so if desired we can fit the afore mentioned link across the terminals to provide plants with years of trouble free nuisence tripping

    M

  9. #9
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    Re: Oil Pressure Differential Switches

    I have had to do numerous rebuilds due to people resetting oil switches without sorting the fault, and you are suggesting letting the plant commit suicide itself, without human intervention.
    No, I am suggesting automatic reset within compressor-safe parameters. This will save the product in scenarios where the fault is temporary and/or intermittant. This could/should be coupled with an alarm to indicate that the switch has tripped. Limiting the number of restarts would cover the more serious faults.
    Last edited by Gary; 22-02-2007 at 05:14 PM.

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    Re: Oil Pressure Differential Switches

    are you presuminmg that on auto reset the compressor will pull the product down to temp in the two minutes of running?
    Obviously it will not. Unless the fault is temporary/intermittant... in which case the compressor will have sufficient net oil pressure to continue running and the product will be saved.
    Last edited by Gary; 22-02-2007 at 05:44 PM.

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    Re: Oil Pressure Differential Switches

    Copeland's approved oil pressure safety controls are
    PENN-P45/RANCO-P30/AND ROBERTSHAW-PD21, There are models with alarm option you have to check your controller voltage and trip out delay time for to select a replacement,
    Penn controls are made by JONSON CONTROLS try to visit their site.
    malik55

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    Re: Oil Pressure Differential Switches

    Even Better is the wiring diagram on the inside of the switch cover

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    Re: Oil Pressure Differential Switches

    yes, Most controllers comes with W.D in side the covers but if it is not there , OPSW it is not a very complicated controller.
    malik55

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    Re: Oil Pressure Differential Switches

    Quote Originally Posted by Gary View Post
    What the world needs is an oil pressure switch that will reset itself after about an hour. An hour is more than enough off time to protect the compressor and this could save a lot of products.

    Maybe if it still activated an alarm and could only do a auto reset once but only if the customer was fully informed of the consequences but I would not like to do it all. I would prefer to invest time into testing the system and finding the cause of the intermmitent fault. The customer is a lot happier if you don't blow up their compressors.
    I came across a maintenance man who throught if would be OK to put and auto reset on a oil failure fault. Several weeks later a real oil problem occured and the compressor kepted reseting itself until it broke all it internals due to lack of oil. The customers production was down and out of pocket by tens of thousands of dollars. Customers don't pay us to do half ass jobs, they pay for a proper job.

    Mike quote of the day. " You are only as good as your last job"

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    Re: Oil Pressure Differential Switches

    Quote Originally Posted by Mike W View Post
    I came across a maintenance man who throught if would be OK to put and auto reset on a oil failure fault. Several weeks later a real oil problem occured and the compressor kepted reseting itself until it broke all it internals due to lack of oil. The customers production was down and out of pocket by tens of thousands of dollars. Customers don't pay us to do half ass jobs, they pay for a proper job.

    Mike quote of the day. " You are only as good as your last job"
    I'm assuming the auto reset you describe did not have a one hour interval, nor did it have a three reset limit, nor an alarm? So your anecdote does not apply.

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    Re: Oil Pressure Differential Switches

    Quote Originally Posted by Gary View Post
    I'm assuming the auto reset you describe did not have a one hour interval, nor did it have a three reset limit, nor an alarm? So your anecdote does not apply.

    Hi Gary.

    In principle I'm not against auto resets under the right restrictions.
    With the reset restrictions you describe I would be tempted to agree that it would stop a lot of wasted callouts (less overtime ).
    I do not know of a switch like you describe is there a switch or is it somthing you are personaly toying with?

    Cheers taz.

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    Re: Oil Pressure Differential Switches

    Quote Originally Posted by taz24 View Post
    Hi Gary.

    In principle I'm not against auto resets under the right restrictions.
    With the reset restrictions you describe I would be tempted to agree that it would stop a lot of wasted callouts (less overtime ).
    I do not know of a switch like you describe is there a switch or is it somthing you are personaly toying with?

    Cheers taz.
    It is simply an idea I am throwing out here in case the control manufacturers are tuning in. Given today's electronics, perhaps it is time to re-think the oil pressure control... and the high pressure control as well.

    I am not so much concerned with reducing overtime as I am with saving the products.

  18. #18
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    Re: Oil Pressure Differential Switches

    Gary
    no disrespect the reason for the safety controls on any system is to protect the equipment from destroying itself mainly due to the customer not being willing to maintain it correctly normally due to the cost. If the customer loses product due to this he only has himself to blame and allowing him to get away with not maintaining his equipment by fitting systems that mean he can have even less engineering input defeats the whole object of what we as engineers are out there trying to do.

    Sorry I think the whole idea is crazy.

    Ian

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    Re: Oil Pressure Differential Switches

    i think gary is just making us discuss a problem that has been apparant for years ie meddling customers and badly trained refrigeration engineers who see something tripped and press every button available to try and get the plant up and running again so they can get home in time for neighbours or other such crap. as a refrigeration engineer it is my job to find the cause of such a trip even if it is intermittent and cure the problem. my secondary consideration is the fate of the product even if that is as a direct result of my action or inaction in solving the aforementioned problem.
    if the problem is that intermittent it never does any harm in keeping proper fault records so that such a fault can be recorded and noted for a future investigation. one day that intermittent fault is going to cause a catastrophic failure and massive cost and i would rather not fit a switch that allows a system to restart 3 times, ignore the oil pressure for up to 2 minutes each time at 1450rpm leading to the compressor requiring a rebuild instead of an oil change/filter clean etc.
    like i said before i really dont think he's serious is he ????

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    Re: Oil Pressure Differential Switches

    Bill
    serious or not you and I think along the same lines in that the health of the equipment is paramount because if that fails the product is wasted anyway. I agree with you that there are lots of so called engineers that do what you mentioned, I do not specifally blame these engineers it is the fact that there is to much work for the guys at the coal face so corners are cut. Gary probably has never had to take the crank out of a Grasso RC11 because some fiddler had decided to keep resetting the oil pressure switch instead of calling for the engineer who would have changed the oil filter in about twenty minutes with no long term damage.

    Ian

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    Re: Oil Pressure Differential Switches

    Quote Originally Posted by Pooh View Post
    Bill
    serious or not you and I think along the same lines in that the health of the equipment is paramount because if that fails the product is wasted anyway. I agree with you that there are lots of so called engineers that do what you mentioned, I do not specifally blame these engineers it is the fact that there is to much work for the guys at the coal face so corners are cut. Gary probably has never had to take the crank out of a Grasso RC11 because some fiddler had decided to keep resetting the oil pressure switch instead of calling for the engineer who would have changed the oil filter in about twenty minutes with no long term damage.

    Ian
    Yes... we all know that frequent resets can destroy the compressor... but that isn't what we are talking about, is it?

    We are talking about 3 resets max, with an hour in between and an alarm to let the customer know something is wrong.

    BTW, I've been a service tech for almost 40 years, on everything from fractional to 3600 ton centrifugals and I've removed lots of cranks.

  22. #22
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    Re: Oil Pressure Differential Switches

    so basically you are changing the priority of the refrigeration tech to product preservation.

    assuming the switch will lock out after 3 resets over 3 hours, there is nothing to stop the customer from powering down the control to effectively reboot the switch and giving the customer another 3 starts etc. ok yes it is at his own risk product wise but at the sharp end we are the ones who will get the denial of inteference and on a fully comp contract i would not want to take that risk.

    theoretically it is not altogether without merit but in practice, if i saw one fitted to one of our customer's pieces of equipment i would be sorely tempted to remove it and fit a manual reset ops and a lockout circuit inside the control panel.
    the temptation on a friday afternoon to reset a switch such as this would be too great for some engineers to resist the urge to reset and bugger off home, leaving the problem for the standby engineer and as sad as it may seem, with the skills shortage this industry is suffering from this would happen too frequently.
    high end equipment with high end engineers is a different situation however and in an ideal situation such a switch is not beyond the realms of possibility.

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    Re: Oil Pressure Differential Switches

    Quote Originally Posted by Gary View Post
    It is simply an idea I am throwing out here in case the control manufacturers are tuning in. Given today's electronics, perhaps it is time to re-think the oil pressure control... and the high pressure control as well.

    I am not so much concerned with reducing overtime as I am with saving the products.
    Some chillers have something similar. You can set the amount of times an electronic reset of oil, hp or lp. After a half dozen times or so the plant locks that compressor out and you need a password to unlock it.

    Kind Regards Andy
    If you can't fix it leave it that no one else will

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    Re: Oil Pressure Differential Switches

    Quote Originally Posted by malik55 View Post
    Copeland's approved oil pressure safety controls are
    PENN-P45/RANCO-P30/AND ROBERTSHAW-PD21, There are models with alarm option you have to check your controller voltage and trip out delay time for to select a replacement,
    Penn controls are made by JONSON CONTROLS try to visit their site.
    malik55
    where would you fit an oil pressure differential switch?

    on what type of system do you use oil diffrential switch?

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    Re: Oil Pressure Differential Switches

    the oil pressure diff switch, is piped up to the suction and the oil pressure if the oil pressure is not40psi over the suction psi after 90 seconds the comp trips out, if its wired up corectly, so to test, drop the 3ph supply to contactors set for cooling, contactor should drop out <after 90seconds< well thats how they used to work,?

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