Just a thought r.e. inpipes reducing flow.

Discussion in 'Filters, Filtration and Pumps' started by GreenNeedle, 18 Oct 2008.

  1. GreenNeedle

    GreenNeedle Member

    Messages:
    2,706
    Location:
    Lincoln UK
    Thinking out aloud (or in typeface. lol)

    I was wondering if when we change the in/out pipes from our filter's supplied ones if it could mean a reduced lph.

    I am specifically thinking of my Tetratec where I replaced the pipes with glass ones. The Lily outflow shouldn't make a difference but the difference between the inpipes are noticeable in that the one supplied has a huge area at the bottom where the water comes in whereas the glass one just has a slit along the bottom and 2 holes just above.

    Could this limit the amount of water that can get through? or does it just mean that the water has to come through the smaller holes with much more force?

    AC
     
  2. The manufacturer's rated LPH will likely be done with no pipework at all, just the pump. Any inlet will reduce the flow, but some more than others.

    Tom
     
  3. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

    Messages:
    8,952
    Location:
    Chicago, USA
    Yep, it sure can. Anywhere in the flow path where the cross sectional area is reduced causes a back pressure against the impeller blades and restricts the flow. Even if somewhere downstream of the restriction the cross sectional area then increases this will not compensate for the loss of momentum. Any restriction in the flow path causes loss of mass flow rate. This includes pinched hoses, bends in pipework and of course, media, dirt or other obstructions inside the filter itself. So if the replacement pipe has a smaller cross sectional area anywhere along it's profile than the stock pipe then flow will be reduced.

    To compare the inlet diameter of the glass pipe you'd have to calculate the areas of the slits + holes and compare with the area of the original pipe opening. You might find that the total areas are similar, just distributed differently. Ultimately, it's easy to see if there is an appreciable difference by simply installing different inlet pipes and comparing the time it takes to fill a jug to a certain volume at the outlet side.

    Cheers,
     
  4. GreenNeedle

    GreenNeedle Member

    Messages:
    2,706
    Location:
    Lincoln UK
    The original pipe had the usual 'cup' style fitment at the end with slits around its circumference. This is much much more than the slit along the bottom of the glass one:

    The Glass one just has the slit along the bottom and then a single 3mm hole just above the ball either side left and right:
    glassin.jpg

    The original has a huge input area in comparison:
    In-Outplastic.jpg

    AC
     
  5. GreenNeedle

    GreenNeedle Member

    Messages:
    2,706
    Location:
    Lincoln UK
    Another thought. theoretically when we add any non standard pipes where the hose fits over it we are reducing flow as the pipe is much thinner inside diameter than the hose and pipe it replaced is?

    Thinking particularly on glass pipes again where the internal diameter of the pipe is 8mm (outside is 12/13) whereas the original pipes were the same internal diameter as the hose (12/13) although where they attach by way of the usual screw fastening may be similar to the 8mm. This of course is only a 2cm or so section so would this small section of smaller diameter restrict flow in the same way as a 45cm section of smaller diameter?

    Am I getting carried away trying to 'pinch' (or return seeing as I am looking at the original fittings) some extra flow that isn't there?

    AC
     
  6. Ray

    Ray Member

    Messages:
    474
    Location:
    Switzerland
    No, I don't think you are. My tank is hard plumbed and even with an inline reactor I get 75% of the rated flow which from what I read on here is a very high value. I think this is because I don't have to negotiate 2 shepherds crooks and instead blast through a bulkhead and up/down a 20mm pipe. Unfortunately I hate fiddling with plumbing so much I can't face swapping the original fittings in to see if they are worse than my bulkheads!

    Also I found out by accident obstructions on the inflow are as important as the outflow, which suprised me since I thought gravity and siphon effects would handle that. Mind you, a lot of the big Eheim filters actually have a larger input than output for some reason?
     
  7. GreenNeedle

    GreenNeedle Member

    Messages:
    2,706
    Location:
    Lincoln UK
    Several hours after writing the last post I thought for a second and then set about returning the original spraybar and inlet that came with the tank with dramatic effect.

    Although not as aesthetically pleasing to the eye as the glassware, the Tetratec's 'stock' pipes are quite nice and reasonably transparent. The flow was more immediately and by a noticeable amount. The filter was outcompeting the 400lph powerhead for a change.

    Maybe I have turned a corner in the 'bling over practicality' argument. I think I will stop buying things just because they look nice and from now on think about if it works as well or better than the original.

    I also 'copied' Zig and have one of the Boyu inline diffusers in the link now and I must say it works very well and I look forward to not having to clean the Rhinox every week. lol. The Rhinox did work very well but weekly cleaning is a bane!!

    Maybe worth others looking at their pipe options on glassware v stock etc. maybe we are all reducing our flow for no reason in the name of beauty!!!

    AC
     

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