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  1. #1
    Join Date
    Apr 2004
    Posts
    161
    I was wondering if someone could shed some light on installing p-traps(and line sets) in suction lines on coolers/freezers.

    Was helping Refrigeration Techs install piping(hard pipe) from new Bohn condensing units(New Bohn R404a and scroll comp med temp) to evap in walkin cooler. The condensing unit is at same level as cooler floor(below evap), approx 70 ft away horizontally.

    The line set from evap runs up thru top of cooler then immediatly 90's horizontally to pipe run to condensing unit. The rise from evap to that 90 is about 30".

    Not being an real experienced refer guy, had a few questions reguarding oil return to condensing units in general.

    We installed trap in suction line down by evap. Was the trap nessasary? Im sure it didnt hurt installing it, just wondering.

    I noticed the hard pipe runs were not pitched one way or the other, does that matter?

    I also noticed the hard pipe seemed to me not very well supported, there were some sags in lines, supports for line sets was about every 10ft. Are the sags just another oil trap or detrimental to oil return on 70' run on 404a system w/scroll comp?

    Is oil return/trapping w/newer refrigerants/compressors more or less important/critical than on older systems/compressors that would use r12/r502?

    Thanks for any responses!

  2. #2
    Join Date
    May 2004
    Posts
    7
    Traps should be installed for every 10' of rise. Installing a trap for less than 10', although may not be needed , can never be a bad thing. Pipe should be supported every 6' ( depending on the local codes ) Oil trapping is an issue no matter which refrigerant your using. In my experience small sags in the lineset won't matter much as long as they're not too drastic.

  3. #3
    Join Date
    Jan 2004
    Location
    Earth
    Posts
    4,879
    Your lines should always be sloped toward the compressor. Unless they are heat reclaim or condenser lines these should be level. It takes energy to move oil. If gravity is your energy source, this is a good thing, gravity is free.


    A Diamond is just a piece of coal, that made good under pressure!

  4. #4
    People always have the thought in their heads there will be time in the future to make ammends once the system is online and they are paid and have gone home.

    Bull.... if people spent more time on the piping and general overall INSTALLATION of a system, there would be less work in the future and less problems!!!

    A poorly piped system is common place today, just as it was forty years ago.
    Only dif being ...we the mechanincs know more today than they did forty years ago, for the most part. And we have the means to correct some of these problems.

    That long ago, most men were afraid to argue with their boss or the top engineers. They were afraid of being drummed out, "black-balled".

    Today, with "hind-sight" working in our favor ... we can point out chapter and verse of where the system problems are located .... to the exact detail.



    If it takes an hour to pump down a circuit on a rack to inspect the TX inlet screen .... that is ONE HOUR which can never ever be recovered! NEVER! It's GONE!!!

    And when Summer is here in full swing ... we wont be having the luxury of too many of those hour long pump down "breaks" while we go grab a cold drink of water or make some phone calls ... awaiting the rack to do it's thing...

    We need the systems engineered corectly, right from the gate!
    Had someone from Henry Valve company been on the job, working alongside the "engineers" who designed the systems ... Henry would have insisted on installing shut off valves at each and every evaporator coil.

    It would have cut down the maintenance time, on a simple screen check, by a factor of four to one. If Not More!!!
    And what's the price of a valve? $25!


    Piping ... do it right ... right now ... or pay continually for the rest of the system's exhistance!!!


  5. #5
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,359

    Traps......etc

    No trap at all is sometimes better than and over sized or improperly located trap. A typical walk-in cooler installation like yours with a piping run as you describe can have several areas where the piping can get screwed up.

    The first thing that's often messed up is the line sizing. Guys will size piping based on evaporator or condensing unit connection sizes instead of opening the book and using the line sizing data for the refrigerant, capacity and conditions of service for the job. This results in oversized lines, oversized traps and poor oil return. (Or worse......intermittent oil return, as in slugs).

    Then they remember reading the book once where it calls for a trap at the outlet of the evaporator. It's usually installed too close to the outlet stub to properly mount the TXV bulb so the bulb gets improperly mounted on the riser somewhere after the trap (there's two more no-no's). I like to leave at least 6" of straight pipe out of the coil (after properly reducing as needed) to mount the bulb at 4 or 8 o'clock and then trap after that.

    If there's two evaps to be piped together, I see a lot of the suction lines get piped to a bullhead tee (another bad move). Instead, drop down to a horizontal run along the wall and pick up the next evap with a side entry tee sized for the combined load at that point. Continue the horizontal (pitched 1/8" per ft toward the compressor, of course) and to your riser. If it's properly sized and less than a four foot riser, no trap is necessary.

    All piping should be supported so there is no significant sag. This means that the sag should not overcome the 1/8" per foot pitch of the run or you're going to hinder good oil return. There are tables available to look up the proper spacing of pipe hangers. If I find one on-line, I'll post a link. Generally for smaller sizes under 1/1/8", 4-6 ft is good. 1 1/8" to 1/5/8" is more like every 8 ft or so.


  6. #6
    The trap will never hurt if it is the right size. In your case I do not think I would have installed the trap.

    One other note on traps. They should be sized to the diameter of the incomming pipe. If the riser requires a drop in size, bush the outlet of the trap.

  7. #7
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,359
    Reduced riser sizing doesn't come until the next chapter.

    I'll always reduce ahead of the trap, but now you've placed a seed of doubt so I'll have to look that up.

  8. #8
    Two problems reducing the trap to the riser size. Excess pressure drop from the trap and the oil has to climb up to get into the trap unless you are paying premium for eccentric reducers.

  9. #9
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,359

    refer dude.......

    No need to look it up. You are right on that one. I must have been experiencing an early "senior moment".

    The older I get, the better I was.

  10. #10
    Join Date
    Jan 2004
    Location
    Earth
    Posts
    4,879
    The trap should always be the size of your horizontal run. Your invert, if used should be riser size.
    ]
    The only time you don't trap a coil. Is if your suction line goes directly down out of the evap. Otherwise you need to trap your coil. This will prevent your coil from becoming the trap.

    I have seen many systems return oil just fine with no trap. But when your coil is your trap, your efficiency suffers.
    A Diamond is just a piece of coal, that made good under pressure!

  11. #11
    Join Date
    Apr 2004
    Posts
    161
    Thank You all for the responses! It is much appreciated. After reading I can certainly see we didnt do the piping the correct way, I kinda figured that refer piping was goofy, its just been years and years of RTU's Ive delt with and usually I dont have to think about oil return.

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