Hydraulic Pump - industrial applications

[mgmrw]

So, sat here confusing myself with Google info after a chaotic day and wondered if there's any engineering geeks on here?

If so, how about this...

18m deep well. Water in he bottom 6m. From the top of the well to the discharge point, its 300m horizontal, and 30-50m elevation.

PROBLEM:

Pump too slowly, water doesn't get out the well and to the discharge point.

Pump too fast, and I empty the well, quicker than it can flow in from the surrounding land.

QUESTION:

Is it possible, to pump slowly, yet maintain pressure on the discharge?


I've spent 6 weeks consulting "experts" and get either all or nothing....

[collector]

you need a speed controller and dial in the pump speed, going that way you can adapt to different needs if need be

[mgmrw]

Jan 28, 2016 21:20:37 GMT collector said:

you need a speed controller and dial in the pump speed, going that way you can adapt to different needs if need be

Will talk to pump engineering firm. That was my thoughts, but was concerned I'd lose pressure if we dropped flow.

[dodgerover]

Can you pump to a large header tank - depending on your flow requirements you could use an IBC then control your existing pump with a level switch, having the header tank would mean you maintain pretty much constant pressure?

[1mzmk1]

When you say, pump too slowly/too fast etc, what are you using to control that at the moment?

It sounds to me like you could regulate flow by restricting the outlet at the end of the pipework whatever that is going into? That way the pump can be driven fast enough to generate the pressure you need to get it where its going, and then limit flow via a valve at the destination to a point that the land can saturate the well quickly enough.

Pumping slowly and maintaining pressure will depend on the type of pump, centrifugal etc. I'm no expert, just a plumber... but we do have a bit of land with a borehole and small pump which supplies a tank and then another larger pump feeding an irrigation system from that.

[mgmrw]

Cheers for the help folks.

After consulting the pump firm,it appears dropping the rate isn't an option as effectively we'll lose up hill shove, which isn't an option.

So at (moderate expense) its time for minimum and maximum floats to indicate levels.

That way the pump can fire up, pump merrily. And cut off when we're dry.

In theory, should be the ticket.

[Dorset_Clive]

What about something like this www.toolstation.com/m/part.html?p=33192 ?

Can only pump to 8m head, so may not be suitable but comes complete with a built in float switch.

[dodgerover]

Feb 1, 2016 12:08:32 GMT mgmrw said:

Cheers for the help folks.

After consulting the pump firm,it appears dropping the rate isn't an option as effectively we'll lose up hill shove, which isn't an option.

So at (moderate expense) its time for minimum and maximum floats to indicate levels.

That way the pump can fire up, pump merrily. And cut off when we're dry.

In theory, should be the ticket.

Does it have to be automated? If not you could use a pipe with a rod down the centre and a large float on the bottom, fix the larger bore pipe to the wall and allow the rod to slide freely inside it, as long as part of the rod pokes out of the top at minimum water level you could put a marker on this to allow you to cut the pump off before running dry.

You could probably automate it as well but i'm not sure how to do it with 240v and avoid the pump cutting in and out continually whilst maintaining minimum water level

[beejay]

Feb 1, 2016 12:08:32 GMT mgmrw said:

Cheers for the help folks.

After consulting the pump firm,it appears dropping the rate isn't an option as effectively we'll lose up hill shove, which isn't an option.

So at (moderate expense) its time for minimum and maximum floats to indicate levels.

That way the pump can fire up, pump merrily. And cut off when we're dry.

In theory, should be the ticket.

I would say (based on some theoretical experience, not so much practical!) that dropping the pump speed should work but there is a bit to it.

For your system you should be able to construct a curve of system head vs mass flow rate. this would start at 68m at zero mass flow rate and rise as mass flow increases (as frictional losses in your pipework increase with mass flow rate and require additional head to overcome). You can then overlay a pump curve; for example for a centrifugal pump, at a fixed RPM, the pump head decreases as mass flow rates increase. Where the pump curve crosses the system curve determines the mass flow rate and head loss required to achieve this.

If you don't have a pump already, then you should be able to select a pump curve that works at the mass flow rate required. You can also play with certain pump parameters (impeller RPM being as easy one) to shift the pump curve around such that you get the mass flow rate you want. However, there are limits to what speeds you can run centrifugal pumps in order to avoid cavitation and there will be areas of the pump curve which will result in running inefficiently.

If you already have this all set up with a centrifugal pump (which sounds the case?) then adding a throttle valve in the outlet pipework might work. This would raise the system head curve and move the operating point to a lower mass flow rate. Again checking where this puts you on the pump curve would be useful to avoid areas you shouldn't be operating in.

If you're still selecting a pump, maybe a positive displacement pump would be more suitable? Driven at a fixed RPM they will pump water at a fixed mass flow rate, generating whatever head is required at the output to achieve this. There will be mechanical limits to the maximum head (output pressure) they can handle though, will need to pick one that suits your situation. Would also suggest a pressure relief in case of blockage in the outlet pipework. With a variable motor drive you should be able to tune it to give the required mass flow rate.

In any case I would think you would want the ability to measure water level to ensure the pump doesn't run dry. There will also be a minimum required inlet pressure which (I think!) would require a minimum head of water above the pump inlet to achieve.

Given this sounds like you're pumping water from a well, I guess you'd want to filter to a point as well. I don't know much about pumping in these circumstances and whether the water quality (particulates and sediment) would have a bearing on pump selection.

Good luck with the project

[mgmrw]

Thanks guys. Its a 18m deep well, the leachate has a certain amount of suspended solids in it, including clay.

So the pump folks came out again yesterday and we now have:

35bhp pump power pack at the top (diesel), then 25m of hydraulic lines leading to a 4" hydraulic head.

Discharge up the well is via 1x continuous 111mm solid pipe to the top of the well. Then a flexi (6m) before joining 250m of 111mm solid discharge pipe.

I also have 2x floats c/w 25m lines. 1 will be set today at 18m, about 0.6m from the cell base. The other will be set at around 16m.

In theory all should be automatic then. Which is a plus as its in the middle of a quarry, 3 miles from our office. So visiting 8 times a day would be a ball ache.

[hario]

The header pipe would also have a series of check valves at the bottom to maintain the prime in the pipework, so to avoid the pump having to re-prime the length of well head every time.