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I'm terribly new at this and have no idea what I'm doing so please do bear with me.

I have a submersible pump that I want to use in a small rainwater tank to water my garden either through your standard 12mm hose or a 13 - 15mm irrigation pipes (all working ok with our tap at home).

When I tried it on a sprinkler using a 12mm hose, the pressure is a fraction of what I normally get. This is currently how I have set it up. (which I have a feeling is the problem)

I replaced the connector that points upwards (see original photo from link) and replaced it with a 32mm to 20mm reducer (A) so I can fit my hose (B) which is ~10m long.

Any suggestions/thoughts on what I should be doing whether having a more powerful pump or correctly configuring the connectors and pipes etc?

I would highly appreciate the physics side of it as well so I can apply this knowledge elsewhere.

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    Sump pumps are usually low pressure compared to house systems. For using to water a garden, would try a drip irrigation system instead of a sprinkler. – crip659 Feb 23 at 20:08
  • Unless you need to spend more money, what you have now should work, but not the sprinkler. Weeping/drip irrigation is usually considered better for gardens anyway. Saves water by putting it where it does most good. – crip659 Feb 23 at 22:04
  • Cheers, thanks for that! – Raderadera Feb 23 at 22:45
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Those pumps are rated in feet or meters of head pressure. Most submersible pumps similar to what you show are only rated to 15-20’ of head this is the equivalent of 7-10 psi or the maximum pressure it can develop. For that amountc of power it draws it probably has a fair volume.

To get more pressure you usually have to sacrifice volume or add horse power. You may not need the gallons per minute and reducing this for a pump that could pump 60 feet of head pressure or more will provide the spray you are after. A pump that can only pump 10 gallons per minute at 60’ of head pressure may be similar in power as your existing pump but spray closer to what you are used to.

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  • Thanks for that, it's very useful. Just double checking when you mean sacrificing volume here, that's what you mean to spray closer to what I'm used to? ie. shorter hose, lesser water? – Raderadera Feb 23 at 22:35
  • With the old pump it could only spray probably a few feet lots of volume. I pump that is rated for a higher head will have more pressure. Most home faucets outside are between 5-10 gallons a minute but the pressure is usually 40-80 psi so it can spray a long distance. If horizontal the length being 10’ or 50’ will not make much difference once pressure is built up by a nozzle if you exceed the flow rate of the pump the pressure will drop off. – Ed Beal Feb 23 at 23:08
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How does it work with just the hose and no sprinkler? That pump probably doesn't have enough pressure to push water through a sprinkler.

Here's a back of the envelope analysis. The pump is spec'd as having a lift of 6 m, which is ~19.8 ft. A column of water with a cross section of 1 sq inch and 2.31 feet high weighs 1 lb, or 1 psi for every 2.31 feet of water height. So that "lift" spec of 19.8 ft is equivalent to 8.6 psi. Household water pressures are usually 30 psi or greater. So the pressure out of that pump is only 1/4 of your typical household water pressure.

If you want to drive a sprinkler, you need a much more powerful pump.

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  • Thanks for that explanation. The hose with no sprinkler gets water through but definitely reduced pressure in comparison (the same as the sprinkler). So just double checking, there is nothing wrong with the way I'm setting it up, it comes down to needing more power based on your calculations – Raderadera Feb 23 at 22:32
  • Yes. Like me and Ed Beal said, basically you need a more powerful pump (bigger head) to do what you want. – SteveSh Feb 23 at 22:37

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