Available Static Head is Sufficient or Pump is required
Available Static Head is Sufficient or Pump is required
(OP)
Dear friends,
Cooling water return header pressure is 1.2 kscg (at ground level). From this point, a tapping is to be taken to take 200 M3/hr of water to a distance of 650 mts(for further treatment). Following is the piping layout:
90°C bend - 35 Nos.
45 °C bend - 5 Nos.
Gate valves - 2 Nos.
Tees - 2 Nos.
Check valves - 2 Nos.
Exit - 1 No.
Entrance - 1 No.
At the discharge point alone, the elevation is 4.0 mts from ground level. Total head loss calculated to be 31.9 ft water column inclusive of elevation. Now the head available is 7.6feet(39.5-31.9)water column. This 7.6 ft head is sufficient or I have to take a tapping from CW pump discharge (pressure is 3 kscg) for this application.
Please advise.
Cooling water return header pressure is 1.2 kscg (at ground level). From this point, a tapping is to be taken to take 200 M3/hr of water to a distance of 650 mts(for further treatment). Following is the piping layout:
90°C bend - 35 Nos.
45 °C bend - 5 Nos.
Gate valves - 2 Nos.
Tees - 2 Nos.
Check valves - 2 Nos.
Exit - 1 No.
Entrance - 1 No.
At the discharge point alone, the elevation is 4.0 mts from ground level. Total head loss calculated to be 31.9 ft water column inclusive of elevation. Now the head available is 7.6feet(39.5-31.9)water column. This 7.6 ft head is sufficient or I have to take a tapping from CW pump discharge (pressure is 3 kscg) for this application.
Please advise.





RE: Available Static Head is Sufficient or Pump is required
Do you want to control the flowrate at 200 m3/hr? In other words, are you going to install a flow meter and a control valve in the line?
RE: Available Static Head is Sufficient or Pump is required
RE: Available Static Head is Sufficient or Pump is required
Line ize is 12 Inches,HDPE
I want to control the flowrate at 200 m3/hr
My concern is whether I will get 200 m3/hr for the available head of 7.6 feet.
Thanks in advance
RE: Available Static Head is Sufficient or Pump is required
With following guidelines for control valve pressure drop:
Delta P Control Valve >= 0.25 x Delta P Static
Delta P Control Valve >= 0.33 x Delta P Friction
Using your numbers, this means that pressure drop over control valve must be minimum 0.25 x( 39.5-13.1) = 6.6 ft water column. Since you have available 7.4 ft water column, you have 7.4 - 6.6 = 0.8 ft water column left for your flow measurement.
RE: Available Static Head is Sufficient or Pump is required
Delta P control valve >= 0.7 bar at maximum flow.
0.7 bar equals about 23 ft of water column, so this will be difficult if your numbers are correct.
RE: Available Static Head is Sufficient or Pump is required
Thanks for your replies.
(1)The line dia is 9.7" -HDPE, not 12"
(2)I am quite sure,line loss is 31.9 ft WC
(3)Now the available head is(39.5-31.9)=7.58 feet
(3A)WC left for flow measurement=7.58-.25x(39.5-13.1)=.98'WC
(4)I think the following definition is self understandable
Del P Control Valve >=.25x(available head-static head)
(5)Could you please give the second equation also in the same above format.
(6)Is it correct:
Del P Contl Valve>=.33(avalble head - tot line frict loss)
(7)>=:Does it mean greater than or equal to
Please give your comments
RE: Available Static Head is Sufficient or Pump is required
(5) Second Equation is:
Delta P >= 0.33(total line friction loss)
So in this case:
Delta P >= 0.33x(31.9 - 13.1)=6.2 ft WC
Which is less stringent than the first equation, but most stringent "rule" is that Delta P >= 0.7 bar!
(7) >= indeed means greater than or equal to, but since we are dealing with "rules of thumb" here, I could as well have written just >
Note that these are just rules of thumb. Maybe you should check with an instrumentation vendor to see what is possible. In your case it may be more economic to spend some extra money for a special valve/flow measurement to save the pump. It may also depend on whether you want to tightly control this flow of 200 m3/hr, or whether some less perfect control would be acceptable.
RE: Available Static Head is Sufficient or Pump is required
You state the 31.9 ft line loss is inclusive of elevation so that is taken cae of. 31.9 ft is 9.7 m which is less than 12m available so you will get the flow you need. In fact, if you don't have a control valve or some means of controlling the flow, the actual flow will be about 222 m3/hr.
Note, if the 31.9 m does not include the 4 metre elevation (exclusive of elevation), you have now only 8 m for line losses, less than the 9.7 m you need and the actual flow will be about 182 m3/hr.
If you need 200 m3/hr in this case, you need a larger line or a higher supply pressure.
Note, I have not checked your line loss calculations. You haven't specified if the flow through the tee is through the run or branch and more importantly, it's impossible to accurately estimate the dP through the 2 check valves you have without manufacturer's data.
RE: Available Static Head is Sufficient or Pump is required