Pump limited
Pump limited
(OP)
Hi there!
We have a cooling machine (it operates at -25ºC) which is cooled with water. According to the specifications we need cooling water between 3 and 10 bars (the machine has a valve opening and closing depending of the need) and it consumes 900 L/h at 3 bars. We will pump it from a deposit with the following pump: Lowara Scuba SC 211C
http://doc.lowara.com/lowdata/doc/EN/borehole-td-e...
One can see the curve in the page 11, It has a maximum presume of 8 bars (1200 L/h) and minimum of 3 (4500 L/h).
My question is if this setup will work. The water pump will send water let's say at 7 bars (direct connection with with cooling machine, plastic tube), if the cooling machine in a moment needs only 3, what happens?
I understand one of the following options:
a) the cooling machine valve breaks (think it is strong enough)
b) the pipe breaks (we will use strong pipes)
c) the water pump breaks
d) nothing, the pump respects the cooling machine
What do you think?
A sketch of the setup
http://files.engineering.com/getfile.aspx?folder=d...
Thank you
regards,
We have a cooling machine (it operates at -25ºC) which is cooled with water. According to the specifications we need cooling water between 3 and 10 bars (the machine has a valve opening and closing depending of the need) and it consumes 900 L/h at 3 bars. We will pump it from a deposit with the following pump: Lowara Scuba SC 211C
http://doc.lowara.com/lowdata/doc/EN/borehole-td-e...
One can see the curve in the page 11, It has a maximum presume of 8 bars (1200 L/h) and minimum of 3 (4500 L/h).
My question is if this setup will work. The water pump will send water let's say at 7 bars (direct connection with with cooling machine, plastic tube), if the cooling machine in a moment needs only 3, what happens?
I understand one of the following options:
a) the cooling machine valve breaks (think it is strong enough)
b) the pipe breaks (we will use strong pipes)
c) the water pump breaks
d) nothing, the pump respects the cooling machine
What do you think?
A sketch of the setup
http://files.engineering.com/getfile.aspx?folder=d...
Thank you
regards,





RE: Pump limited
If it does then your system seems to be over powered. Why do you have a pump which has a MINIMUM flow rate of 1200 l/h to feed something which only needs /consumes 900l/h??
You will damage your pump if you operate long term at less than minimum flow and you will use lots more energy than you need to as it is operating very inefficiently.
So it will "work", but after a few months the pump might fail. Everything else seems OK as your pump max pressure is lower than the machine and hopefully your pipe which should be rated at least as high as 10 bar.
If the machine does not control the flow then you could flow much more, but given that the spec seems to say any water pressure is OK between 3 and 10 bar it would seem that the flow control is internal to the machine.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pump limited
The water will be returned to the deposit (and this will be cooled with another small cooling machine)
The flow is too big because it increases as the the head capacity of the pump increases, and we need to be between 3 and 10 bars.
I guess the cooling machine will control also the flow (it takes whatever it needs) so I understand this will damage the water pump as you say.
I'll have to look for a pump with less flow, right?
cheers,
RE: Pump limited
RE: Pump limited
Figure out the load (flow / pressure) first then design the pump to match, not the other way round.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pump limited
Johnny Pellin
RE: Pump limited
JJPellin: Thank you, I was just about to write something similar to your answer to try to pinpoint the problem.
To summarize:
1. Check that the necessary flow figure is correct. AS JJPellin says this will probably correspond to a given flow, at a givin temperature measured at a given point.
2. Sensible to check necessary flow at max, minimum and normal operationoal conditions of the complete system. (Cooling amount for machine corresponding to cooling effect given byi a given amount of water at a given temperature).
3. Check necessary pipeline diameter.
4. Returncircuit to tank probably necessary, to open if pressure is somewhat higer than preset for inlet to cooling system.
5. Select pump to suite capacities.
5. Total circuit will probably feed cooling water into the machine with a temperature controlled valve, wile the pump (soft start/stop) should be operated to upkeep a given pressure. 3-7 bar is to wide and probably upper/lower limit. Select something in between, and safe with retur as in point 4.
RE: Pump limited
It seems the pump adjusts its pressure automatically depending on the needs.
In any case a by-pass seems a good idea to be in the safe side. I will follow your advise.
Thanks for all
regards,
RE: Pump limited
Errr, in a sense it does, but only within a certain range. Your pump is quite rare in having quite a large head range (75 to 35m) though the last one will be at a high flow. Most centrifugal pumps are more like 25% from max to min head before it runs off the curve.
From everything we've seen so far you need a different (smaller) pump once you've worked your system losses out and how flow is controlled. Just putting in any old pump that looks ok will not end well.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way