Submersible pump questions

[Mama Noodle]

3 hours ago, Arjen said:

It is possible you are correct. But it is difficult to believe. 

 

I know for a fact that I am 100% correct because I have been living with wells and pumps my entire life and I have built a career in the oil and gas industry working on pumps and wells. You can believe what you want. 

 

3 hours ago, Arjen said:

I never did the calculations, or the measurements, but it is difficult to believe that an often starting and stopping submersible is less expansive then an often starting and stopping (house) pressure pump. And for my house I made myself an accumulator tank. My pressure pump runs at least one minute when it goes on. 

 

The sub pump and bladder tank if properly sized would only kick on after using 20-30 gallons of water and only kick on for a minute or less to recharge the bladder tank back up. 

 

It is NOT starting and stopping 'often' and if it does it was designed wrong. 

 

You guys can ignore good advice from a professional if you like. No coin out of my wallet. 

 

PS, with a properly sized system you don't need the house pump, storage tank etc saving even more power consumption. 

[Mama Noodle]

 

1 hour ago, bankruatsteve said:

Opening the cover, I find a 25 µF cap which looks OK.  Removed and measured on my DMM where it leveled out at 18.4.  Is it likely this could be the problem?  The previous pump had the winding shorted by the ants and was toast according to the fix-it guy.  

 

You can always try replacing the capacitor and see, nothing wrong with that other than finding one and waiting for it to arrive. 

 

Or you can disassemble the pump and replace just the electric motor, which im sure there are loads locally. 

[bankruatsteve]

42 minutes ago, Mama Noodle said:

The sub pump and bladder tank if properly sized would only kick on after using 20-30 gallons of water and only kick on for a minute or less to recharge the bladder tank back up. 

I keep vacillating on this.  So, Lazada has a 3" 1HP sub-pump with a control box (which is just to start the pump and over-load protection).  It is rated for 25 l/m at 22m head.  Which is exactly what I think I need.  The attached diagram seems to be what you are talking about - and I get it for what would be a domestic supply.  I see that the pressure control switch would start/stop the pump (how to set the pressure?).  I don't see the need for the bladder tank if I would be running pretty much continuously for 1 hour and relying on the pressure switch to off when the faucet is closed. Yes?

 

Forgot the diagram:

Edited April 26, 2020 by bankruatsteve

[Mama Noodle]

Yep that diagram is pretty much what I’m talking about but can be way more simplified. 
 

That 3” pump is pretty weak so if you are just opening a valve and letting water flow directly out of a 3/4” water hose with no sprinklers then you’d probably be fine but if trying to run sprinklers you might run into a problem with over pressure or pump “hammering” 

 

Pressure control switches (for this purpose) have a high and low side that can either be adjusted by turning a set screw and watching your pressure or they make digital ones where you just push buttons and adjust the led set points. Thats easy. 
 

While it’s true that when you turn the tap off, the pump will stop I’m not positive it’s going to work like you think it is. If it builds pressure fast, the switch will kick it off and since you can’t compress water as soon as it kicks off, it’s going to kick back on again because there’s no buffer (bladder tank) which is pump “hammering”. 
 

But that pump is kinda small. Without seeing the curve and knowing your well depth it’s hard to say. It MIGHT work “well enough” without a tank. 
 

Mechanical Switch Example

https://s.lazada.co.th/s.1YbJa

 

Digital Switch Example

https://s.lazada.co.th/s.1Y2jF

 

 

[bankruatsteve]

33 minutes ago, Mama Noodle said:

While it’s true that when you turn the tap off, the pump will stop I’m not positive it’s going to work like you think it is. If it builds pressure fast, the switch will kick it off and since you can’t compress water as soon as it kicks off, it’s going to kick back on again because there’s no buffer (bladder tank) which is pump “hammering”. 

Thanks.  But, not sure I'm following you RE the pressure switch action.  I assume they can be set for pressure you want to turn off the pump and some less pressure to turn the pump back on.  Or not?  So, when I turn off the faucet to the sprinkler, it should build pressure and stop the pump.  Turn the faucet back on, pressure drops and starts the pump.  Yes or not exactly?  If can I set the control (just throwing out some numbers here) to 30 PSI for stop and 20 PSI for start, what would cause the pump to hammer?  I assume the water in the pipe isn't going anywhere so should pretty much retain pressure.  (?)

 

Edit:  Forgot to ask why you think that pump is weak?  The specs from the pump say 25 l/m at 22m head.  Which is exactly what I think I want and have for head.

 

Edited April 26, 2020 by bankruatsteve

[Mama Noodle]

1 hour ago, bankruatsteve said:

But, not sure I'm following you RE the pressure switch action.  I assume they can be set for pressure you want to turn off the pump and some less pressure to turn the pump back on.  Or not?

 

Exactly. They have a high and low pressure cut-in and cut-out settings. 

 

1 hour ago, bankruatsteve said:

So, when I turn off the faucet to the sprinkler, it should build pressure and stop the pump.  Turn the faucet back on, pressure drops and starts the pump.  Yes or not exactly?

 

Yes - BUT - remember there will be no "Building" of pressure. It's not a jet pump. Its going to reach cut-out pressure instantly when the valve is turned off. 

 

1 hour ago, bankruatsteve said:

If can I set the control (just throwing out some numbers here) to 30 PSI for stop and 20 PSI for start, what would cause the pump to hammer?  I assume the water in the pipe isn't going anywhere so should pretty much retain pressure. 

 

35PSI is average pressure for sprinklers and homes. 

Think about it: When you close the valve and no water is flowing its going to be BANG instant high side cut-out. Thats ok I guess if the pressure switch is reactive enough for closing the valve and stopping the pump. The problem arises when you are trying to run sprinklers and the pump. If you are not running enough sprinklers to utilize at or near the full capacity of the pump, its going to fly up to cut-out pressure, shut off, but since the sprinklers are running the pressure is going to instantly drop back down and hit cut-in pressure, then fly back up to cut-out pressure... Over and over and over again. The speed it hammers will be determined by the size of the pump vs amount of sprinklers you're running. 

 

Making sense or not really? Remember the pump is not a slow jet pump, its more instant. 

 

1 hour ago, bankruatsteve said:

Forgot to ask why you think that pump is weak?  The specs from the pump say 25 l/m at 22m head.  Which is exactly what I think I want and have for head.

 

Well those specs are at zero pressure right? Because typically that's how pumps are listed on the tags. Can you show me the link for the pump?

[Mama Noodle]

2 hours ago, bankruatsteve said:

Forgot the diagram:

 

Also, there are a couple of unsafe flaws in that diagram so I wouldn't recommend using it exactly like its sketched, just use it to get an idea of how it works. 

[bankruatsteve]

38 minutes ago, Mama Noodle said:

Well those specs are at zero pressure right? Because typically that's how pumps are listed on the tags. Can you show me the link for the pump?

It doesn't say anything about pressure but the table shows 00 l/m at maximum 57m head.  I assume that would be zero pressure at the head output.  Here's the link, if you can't translate to English, the specs are 1 page down.  The 1st table is l/m and the 2nd table is corresponding head.  Thanks.

https://www.lazada.co.th//products/i3675352-s4496747.html?spm=a2o4m.cart.0.0.660b6108wRyO5B&urlFlag=true

Edited April 26, 2020 by bankruatsteve

[bankruatsteve]

BTW:  My sprinkler handles 25 l/m just fine based on:  I have been watering using my tank and 250W "house" pump.  20 min. uses about 500 liter (maybe a bit less).

 

The jet pump was about the same or maybe a bit less output.  The pressure gauge on the pump would go to about 45 PSI for maximum output but sometimes had to reduce output to get the pressure.

 

 

Edited April 26, 2020 by bankruatsteve

[Mama Noodle]

3 minutes ago, bankruatsteve said:

My sprinkler handles 25 l/m just fine based on:  I have been watering using my tank and 250W "house" pump.  20 min. uses about 500 liter (maybe a bit less).

 

I don't think you're gonna get 25l/m @  30 PSI from that pump you linked to. 

 

If the price isn't a big deal and you want to experiment then why not, you probably won't need a bladder tank either but that's because I think it's going to perform lower than expected. 

 

This pump would be more practical for your application, but its highly likely you'd need a bladder tank:

 

https://www.lazada.co.th/products/4-15-2-multistage-deep-well-submersible-pump-clinton-95qjd5-8012-15-i270177391-s422601216.html?spm=a2o4m.searchlist.list.1.6051251cbytoy0&search=1

[bankruatsteve]

6 minutes ago, Mama Noodle said:

I don't think you're gonna get 25l/m @  30 PSI from that pump you linked to. 

Can you elaborate?  And, where did 30 PSI come from?  I know product specs aren't always real world but have to base on something.  My jet pump is/was 1.5 HP so I don't know why I would want 2 HP from a sub.  Anyway... thank you for your input.  I'll have to think about this more.

[Mama Noodle]

8 minutes ago, bankruatsteve said:

Can you elaborate?  And, where did 30 PSI come from?  I know product specs aren't always real world but have to base on something.

 

You need around 30 psi to operate your sprinklers, correct? The head and flow of the pump you listed is at zero pressure. 

 

So if you take your 25l/m @ zero pressure pump (as listed in the link) and then require the pump to deliver 25l/m @ 30 PSI its not going to happen. Your never going to get 25l/m at 30 PSI, you will get significantly less. 

 

As your desired pressure rises from zero upwards, your required pump head has to rise as well. 

 

13 minutes ago, bankruatsteve said:

My jet pump is/was 1.5 HP so I don't know why I would want 2 HP from a sub.

 

Sorry I read the translation wrong I thought it was a 1.5 hp pump. 

[bankruatsteve]

6 minutes ago, Mama Noodle said:

You need around 30 psi to operate your sprinklers, correct? The head and flow of the pump you listed is at zero pressure. 

Lost me again.  The tables for the pump I linked follow.  At 22m Head, it shows 25 l/m.  That could not possibly be at zero pressure.

 

[Mama Noodle]

59 minutes ago, bankruatsteve said:

At 22m Head, it shows 25 l/m.  That could not possibly be at zero pressure.

 

Thats how the table reads to me, and the fact that at 57m it shows zero flow kind of backs it up. 

 

Its usually assumed that if listed like that its at zero pressure or restriction. Then you calculate your own required head. 

 

Hydraulics is complicated and pump head calculations are confusing but if you want to get it right then it needs to be done. 

[Mama Noodle]

1 hour ago, bankruatsteve said:

Lost me again. 

 

Have a look at this video, ive passed it on to friends before and at the end it has a very basic calculation to workout a rough pump head requirement. 

 

 

[bankruatsteve]

46 minutes ago, Mama Noodle said:

Thats how the table reads to me, and the fact that at 57m it shows zero flow kind of backs it up. 

But, that is at maximum head. OK, thanks again. I think I have enough to go forward. Cheers.