Liquid ring pump as raw water pump, pros and cons?

Discussion in 'DIY Marinizing' started by Nidza, Sep 19, 2017.

  1. Nidza
    Joined: Nov 2016
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    Nidza Junior Member

    Well, I hope I have chosen good place in forum to ask this question.

    During the restoration/renovation planning of my boat, long time ago, my father has chosen not to use original impeller pump for Cummins V-504-M, but rather liquid ring pump Gilkes M 100/350 which was available at that time (in the '80s). Since I have continued restoration/renovation in recent years and finished it, I have decided to use that same pump, it was new, I like the principle of liquid ring very much, seems to me more reliable and less prone to mistakes which can destroy impeller in impeller pumps and so on... Very important for me was that I had the manual for the pump with the characteristic curves so I could calculate appropriate belt pulley diameter to achieve needed waterflow for the engine raw water cooling system (indirect through heat exchanger and then through wet exhausts (risers, waterlocks and tips above water line)). Anyway, I am very satisfied with the pump, it works flawlessly and waterflow is a good match for engine, luckily, with the first calculated pulley since engine temperatures are exactly where they should be according to engine manual. Flow is very steady which is in correspondence with liquid ring pump principal of operation.

    Anyway, since most boats today use commonly impeller pumps, I am curious why is it so? Is there some technical reason or just better price? I know that on some older engines they were used, but not much info on the internet, so I am counting on experienced members view on this. What are technical pros and cons of using liquid ring pump as raw water pump for marine engine? Is there something that I should worry about or just service it regularly and enjoy? Beside greasing, there is not much things to do around it, except in case that it has to go to service due to leaking of some seals. Until now, 220 hours of operation, no problems.
     
  2. hookcap2017
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    hookcap2017 Junior Member

    what is your questions? the water jet appropriate the high speed boat above 25kn.
     
  3. gonzo
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    gonzo Senior Member

    They all seem to be designed to pump gasses not water.
     
  4. baeckmo
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    baeckmo Hydrodynamics

    There is a difference in pump characteristics. Normally, a pump's operating behaviour is described in a diagram, showing pressure ("head") as a function of flow at a given speed. The rubber impeller pump has a more vertical operating curve than the liquid ring pump; ie the flow is less sensitive to pressure variations. The liquid ring pump curve is "falling off" to a greater extent, meaning that for a certain increase of flow resistance it will deliver less flow. As long as you know the system losses that have to be overcome, there is no problem with flow variation, though.

    Both types are "uncomfortable" with sand ingestion; the lr pump due to rather tight tolerances between impeller sides and housing, and the ri pump due to the obvious wear from the rubber "lips" against the housing. They are both self-priming; the lr pump can handle high amounts of gas in the flow (with a loss of liquid flow, of course). As long as the lr pump is pumping reasonably clean water, it will work "forever", provided the impeller, housing and shaft materials are selected correctly regarding corrosion in the actual liquid.

    The lr principle is indeed used for compressors, particularly vacuum-ditos, but the absolute majority of lr pumps are found in domestic water supply, pumping from a local well into the house holding tank (we call them "hydrofor pumps").
     
  5. Nidza
    Joined: Nov 2016
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    Nidza Junior Member

    Thank you Baeckmo.

    So keeping raw water system clean and pump greasing are the most important tasks for protecting the pump. As soon as I have opened characteristics of both pumps I have understood the difference due to head changes. as you have explained.

    I have heard milion times about hydrofor pumps from people building houses in remote places, but have never been interested to investigate what type of pump is it.

    About the materials, pump was made for marine conditions, enclosure and impeller are made of bronze, some bearings of aluminum bronze, shaft from molybdenum stainless steel, so no worries in that direction.
     
  6. baeckmo
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    baeckmo Hydrodynamics

    ...... As soon as I have opened characteristics of both pumps I have understood the difference due to head changes. as you have explained.....
    Fine, and to find the operating point, you add the system characteristics to those pump diagrams. At zero flow there is a small static head (plus or minus less than a meter in a boat installation), and with increasing flow the losses increase with flow^2. The crossing point between delivered and required is the resulting operating point. You often find notes regarding pump data on the pump label, but remember that the operating point is always determined by the system!
     
  7. gonzo
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    gonzo Senior Member

    How is the Liquid ring pump self priming? My understanding is that it need to be primed with some fluid for it to seal.
     
  8. baeckmo
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    baeckmo Hydrodynamics

    It's a question of definition/semantics; in the pumping industry a pump is understood to be self-priming if it is capable to evacuate gas from its suction piping system. And, yes to do so, in most designs the housing has to contain a certain amount of working liquid; in some texts this "filling up" is referred to as "priming the pump", which is not the same as "self-priming capacity" of the pump.
     
  9. gonzo
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    gonzo Senior Member

    That is what I mean. A traditional rubber impeller pump will self prime when it is dry. That is within a maximum head. Looks like the liquid ring pump would have to be installed below the waterline or be hand primed.
     

  10. Nidza
    Joined: Nov 2016
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    Nidza Junior Member

    Yes, self primed centrifugal and liquid ring pumps must be primed for the first time, not possible to start completely dry, but after that for self priming centrifugal pumps it is enough that they have just mixture of water and air and they can "vacuum" the water. So yes, either hand priming either installation under water line, but first priming is really easy (e.g. through water strainer).

    On some other forum I have found out that this pump is actually self-priming centrifugal pump, although in original brochure it says side channel liquid ring type pump, but it seems that it is centrifugal, but has side channel for self priming, so that is from where the confusion came from and also because it has not so typical impeller shape. Also, term side channel pump always brings liquid ring pump when you search the internet.
     
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