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Understanding Pump Head

Pump Head
ပန္ ့တစ္လံုးကို မေရြးခ်ယ္မွီ System အတြက္ လုိအပ္ေသာ flow rate and Total dynamic Head (TDH) ကို သိရွိရန္လုိအပ္သည္။


Head ဆုိသည္မွာ လုိအပ္ေသာ flow amount စီးဆင္းသြားရန္အတြက္ သို့ စီးဆင္းသြားေၾကာင့္ၿဖစ္ေပၚလာေသာ ခုခံအား(resistance) ၿဖစ္သည္။
ပန့္တစ္လံုး၏ ေအာက္ output သည္ 20 head feet ရွိသည္ဟုသည္မွာ ထုိပန့္ မွထြက္လာသည္ ေရကို ေလထဲသို. တည္မတ္စြာလႊတ္လုိက္လွ်င္ ေပ၂၀ အၿမင့္သုိ့ေရာက္သည္ဟုဆုိလုိသည္။

ပန့္မ်ား၏ Head ကို သံုးမ်ိဳး ခြဲၿခားနုိင္သည္

Static Head ဆုိသည္မွာ တြန္းပို့လုိေသာ ေရ ေရာက္ရွိသြားရမည့္ ေဒါင္လုိက္အၿမင့္(vertical distance) ၿဖစ္သည္။

(Static Head, ft) = (Discharge Head, ft) - (Suction Head, ft)

Static Head သည္ Discharge Head ႏွင့္ Suction Head ေပါင္းထားၿခင္းၿဖစ္သည္။

Discharge Head ဆုိသည္မွာ ပန့္၏ Center line ( the pump datum point ဟုလည္းေခၚသည္။) မွ အၿဖည့္ခံကန္ (receiving tank) ၏ ေရမ်က္နွာၿပင္အထိ ေဒါင္လုိက္တုိင္းထားေသာ အၿမင့္ (verticle distance) ၿဖစ္သည္။

Suction Head ဆုိသည္မွာ ပန့္၏ Center line ( the pump datum point ဟုလည္းေခၚသည္။) မွ စုပ္ယူမည့္ ေရမ်က္နွာၿပင္အထိ ေဒါင္လုိက္တုိင္းထားေသာ အၿမင့္ (verticle distance) ၿဖစ္သည္။

စုပ္ယူမည့္ ေရမ်က္နွာၿပင္သည္ပန့္ the pump datum point ၏ အထက္တစ္ေနရာတြင္လည္းၿဖစ္လွ်င္ Positive Suction Head ဟုသတ္မွတ္သည္။

သို့မဟုတ္ စုပ္ယူမည့္ ေရမ်က္နွာၿပင္သည္ပန့္ the pump datum point ၏ အနိမ့္တစ္ေနရာတြင္လည္းၿဖစ္လွ်င္ Negative Suction Head ဟုသတ္မွတ္သည္။

ဥပမာ ၁

ေၿမၿပင္ေပၚတြင္ရွိေသာ ေရကန္တစ္လံုးမွာ အၿမင့္တူညီေသာ ေနာက္ေရကန္တစ္လံုးအတြင္းသို့ပန့္ၿဖင့္ေမာင္းထည့္လွ်င္ထုိ ပန့္၏ static head မွာ သုည ၿဖစ္သည္။ တနည္း static head မရွိေပ။ အဘယ္ေၾကာင့္ဆုိေသာ ေဒါင္လုိက္အၿမင့္(vertical distance) မရွိေသာေၾကာင့္ၿဖစ္သည္။

ဥပမာ၂

ေၿမၿပင္ေပၚတြင္ရွိေသာ ေရကန္တစ္လံုးမွာ ၁၅ ေပအၿမင့္တြင္ရွိေသာ ေရစင္တစ္ခုအတြင္းရွိေရကန္ထဲသို့ ပန့္ၿဖင့္ေမာင္းထည့္လွ်င္ ထုိပန့္၏ static head မွာ 15 ft Head ၿဖစ္သည္။ စုပ္ယူမည့္ ေရမ်က္နွာၿပင္သည္ ပန့္ the pump datum point ႏွင့္ အၿမင့္တူေသာေနရာတြင္ရွိေသာေၾကာင့္ static head (= 0) မရွိေပ။ Suction Head မရွိေသာေၾကာင့္ static headသည္ Discharge head15 ft ႏွင့္တူညီသည္။

 

ဥပမာ ၃

အနက္ ၅ ေပရွိေသာ ေရတြင္းတစ္ခုအတြင္းမွ ေရကို၁၂၅ေပအၿမင့္တြင္ရွိေသာ ေရစင္တစ္ခုအတြင္းရွိေရကန္ထဲသို့ ပန့္ၿဖင့္ေမာင္းထည့္လွ်င္ ထုိပန့္၏ static head မွာ (125, ft) - (-5, ft) = 130ft Head ၿဖစ္သည္။

စုပ္ယူမည့္ ေရမ်က္နွာၿပင္သည္ ပန့္ the pump datum point ထက္အနိမ့္ ၁၀ေပ ေနရာတြင္ရွိေသာေၾကာင့္ Negative Suction Head (-5ft) ၿဖစ္သည္။

(Static Head, ft) = (Discharge Head, ft) - (Suction Head, ft) = (125, ft) - (-5, ft) = 130ft

ဥပမာ ၄

အၿမင့္ ၁၅ ေပရွိေသာ ေရကန္တစ္ခုအတြင္းမွ ေရကို ၂၅ေပအၿမင့္တြင္ရွိေသာ ေရစင္တစ္ခုအတြင္းရွိေရကန္ထဲသို့ ပန့္ၿဖင့္ေမာင္းထည့္လွ်င္ ထုိပန့္၏ static head မွာ (25, ft) - (+15, ft) = 10ft Head ၿဖစ္သည္။

စုပ္ယူမည့္ ေရမ်က္နွာၿပင္သည္ ပန့္ the pump datum point ထက္အၿမင့္ ၁၅ေပ ေနရာတြင္ရွိေသာေၾကာင့္ Positive Suction Head (+15ft) ၿဖစ္သည္။

(Static Head, ft) = (Discharge Head, ft) - (Suction Head, ft) = (25, ft) - (+15, ft) = 10ft

ဥပမာ၅

Cooling Tower တစ္လံုး ၏ Hot water Basin သည္ ပန့္ the pump datum point ထက္ ၁၅ ေပအၿမင့္တြင္ရွိသည္။ Cooling Tower တစ္လံုး ၏ Cool water Basin သည္ ပန့္ the pump datum point ထက္ ၁၀ ေပအၿမင့္တြင္ရွိလွ်င္ ထုိ Cooling Tower တြင္တပ္ဆင္ထားေသာ Condenser Water Pump ၏ Static Head သည္မည္မွ်ၿဖစ္မည္နည္း။

Condenser Water Pump သည္ Cool water Basin မွ ေရကို စုပ္ယူ၍ Chiller မွတဆင့္ Hot water Basinအထိေရာက္ေအာင္တြန္းပို့သည္။ ထုိေၾကာင့္ စုပ္ယူမည့္ ေရမ်က္နွာၿပင္သည္ ပန့္ the pump datum point ထက္အၿမင့္ ၁၀ေပ ေနရာတြင္ရွိေသာေၾကာင့္ Positive Suction Head (+10ft) ၿဖစ္သည္။ Discharge Head မွာ 15ft ၿဖစ္သည္။

(Static Head, ft) = (Discharge Head, ft) - (Suction Head, ft) = (15, ft) - (+10, ft) = 5ft

ဥပမာ ၆

ဥပမာ ၇


Friction Head

Piping system တစ္ခုအတြင္းတြင္ မည္သည့္ အရည္တစ္မ်ိဳး (liquid) စီးဆင္းပါက(flow) ထုိအရည္၏ fluid friction ေၾကာင့္ head or pressure losses ၿဖစ္ေပၚသည္။ ထုိအၿပင္ fluid သည္ piping system အတြင္းတြင္အသံုးၿပဳထာေသာ  valves, strainers, and bends တုိ့မွ ၿဖစ္ေပၚလာေသာ ခုခံအား (resistance) မ်ား မွ လည္း ၿဖစ္ေပၚလာသည္။  

The friction losses မ်ားသည္ ပိုက္ material အမ်ိဳးအစား (the pipe material),  ပိုက္အရွည္ (length of the piping), ပိုက္အတြင္းတြင္ အရည္၏သြားနွုန္း (fluid velocity) ႏွင့္ အရည္၏   properties (properties of the fluid) တုိ့ၿဖစ္သည္။ ထုိေၾကာင့္ ေရ(water) ကဲ့သုိ့အရည္မ်ိဳးသည္ ကို အသံုးၿပဳသည္ water distribution system မ်ားတြင္ minimizing pipe length
and reducing flow velocity (increasing pipe diameter) တုိ့ၿဖင့္ friction losses ကို ေလွ်ာ့ခ်နုိင္သည္။

Major Head Loss - head loss or pressure loss - due to friction in pipes and ducts.

Minor Head Loss - head loss or pressure loss - due to components as valves, bends, tees and the like in the pipe or duct system

Friction losses ဟုလည္း ေခၚသည္

Major Head Losses ဟုလည္း ေခၚသည္။

Dynamic losses ဟုလည္း ေခၚသည္။

Minor Head Losses ဟုလည္း ေခၚသည္။

Pipe Size (flow velocity)
Pipe Length
Pipe material
changes in flow area (Velocity)
Change in Flow Direction
Obstructions

Friction Head = Friction losses သို့ Major Head Losses + Dynamic losses သုိ့ Minor Head Losses

Piping systems မ်ားတြင္ တပ္ဆင္ထားေသာ အမ်ိဳးမ်ိဳးေသာ fittings and devices မ်ားေၾကာင့္ၿဖစ္လာေသာ The Dynamic losses သို့ Minor Head Losses မ်ားၿဖစ္ေပၚသည္။ ထို losses မ်ားပမာဏသည္ fittings and devices မ်ား၏ ဒီဇုိင္းေပၚတြင္မူတည္သည္။ ထုိေၾကာင့္ flow velocity တစ္ခု အတြက္ ဘားပံုစံ(types of valves) မ်ားေၿပာင္းလွ်င္ေၿပာင္းသလုိ ၄င္းတုိ့ႏွင့္သက္ဆုိင္ေသာDynamic losses သို့ Minor Head Losses မ်ားမ်ားလည္းလုိက္၍ေၿပာင္းလဲသည္။ ထုိေၾကာင့္ ဘားပံုစံ(types of valves) မ်ားကို သင့္ေလွ်ာ္ေသာ applications အတြက္ စနစ္တက်ေရႊးခ်ယ္တတ္ရန္လုိအပ္သည္။

 ဥပမာအားၿဖင့္ globe ဘားသည္ (globe type valves) chilled water and condenser water piping systems မ်ားတြင္ အဖြင့္အပိတ္(isolation) မ်ားလုပ္ရန္အတြက္ အမ်ားဆံုးအသံုးၿပဳေလ့ရွိသည္။  ထုိ globe ဘားသည္ လံုးဝပြင့္ေနသည့္အခါ (fully open) မ်ိဳးတြင္ေတာင္မွ high-pressure drop ရွိသည္။ အဘယ္ေၾကာင့္ဆိုေသာ္ globe ဘား၏ တည္ေဆာက္ပံုေၾကာင့္ စီဆင္းမွဳ၏ ဦးတည္ရာေၿပာင္းလဲသြားေသာေၾကာင့္ၿဖစ္သည္။ (to the change in direction the flow). Butterfly valves သည္ လံုးဝပြင့္ေနသည့္အခါ (fully open) တြင္ အနည္းငယ္ေသာ သို့ မေၿပာပေလာက္ေသာ resistance ကိုသာ ၿဖစ္ေစသည္။

Total dynamic head (TDH) - ဆုိသည္မွာ static head, Friction losses(Major Head Losses) ႏွင့္ Dynamic losses (Minor Head Losses) တုိ့ေပါင္းထားၿခင္းပင္ၿဖစ္သည္။ TDH ကို the horsepower calculations အတြက္လည္းသံုးသည္။

 

SUCTION HEAD & TDH PROBLEMS

EXAMPLE: The influent pump discharges into a channel where the liquid level is 14 feet above the pump datum line. The pump draws its suction from a wet well, whose water surface is 5 feet above the pump. The friction head is 5.6 ft.

Determine the Static Head, in feet.

Static Head, ft = (Discharge Elev, ft) - (Suction Elev., ft)

Static Head, ft = (14 ft) - (5 ft) = 9 ft Static Head

Calculate the Total Dynamic Head (TDH), in feet.

TDH = (Static Head, ft) + (Friction Head, ft)

TDH = (9 ft) + ( 5.6 ft) = 14.6 ft TDH

PROBLEM: The influent pump discharges into the grit chamber, where the liquid level is 8 feet above the pump datum line. The pump draws its suction from a wet well, whose water surface is 2 feet above the pump. The friction head is estimated at 2.5 ft.
Determine the Static Head, in feet. (Ans: 6 ft)
Calculate the Total Dynamic Head (TDH), in feet. (Ans: 8.5 ft)

PROBLEM: The polymer makeup pump discharges into the solution tank, where the liquid level is 8 feet above the pump datum line. The pump draws its suction from a sump, whose water surface is 2 feet above the pump. The friction head is 1.5 ft.
Determine the Static Head, in feet. (Ans: 6 ft)
Calculate the Total Dynamic Head (TDH), in feet. (Ans: 7.5 ft)

SUCTION LIFT & TDH PROBLEMS

EXAMPLE: The influent pump discharges into a channel where the liquid level is 14 feet above the pump datum line. The pump draws its suction from a wet well, whose water surface is 3 feet BELOW the pump. The friction head is 6 ft.

Determine the Static Head, in feet.

Static Head, ft = (Discharge Elev, ft) - (Suction Elev., ft)

Static Head, ft = (14 ft) - (-3 ft) = 17 ft Static Head

Calculate the Total Dynamic Head (TDH), in feet.

TDH = (Static Head, ft) + (Friction Head, ft)

TDH = (17 ft) + (6 ft) = 23 ft TDH

PROBLEM: The influent pump discharges into the grit chamber, where the liquid level is 8 feet above the pump datum line. The pump draws its suction from a wet well, whose water surface is 2 feet below the pump. The friction head is estimated at 2.5 ft.
Determine the Static Head, in feet. (Ans: 10 ft)
Calculate the Total Head (TDH), in feet. (Ans: 12.5 ft)

PROBLEM: The raw water pump discharges into the sand trap, where the liquid level is 18 feet above the pump datum line. The pump draws its suction from a sump in the reservoir, whose water surface is 2 feet below the pump. The friction head is estimated at 4 ft.
Determine the Static Head, in feet. (Ans: 20 ft)
Calculate the Total Dynamic Head (TDH), in feet. (Ans: 24 ft)

 


    

Pump ႏွင့္သက္ဆုိင္ေသာ ACMV Lecture မ်ား (7 Lectures)
1 Pumping System Type of Pumps Read
2 Pumping System Pump Head Calculation Read
3 Pumping System Pump Curves Read
4 Pumping System Pump Calculation Examples 1 Read
5 Pumping System Pump Calculation Examples 2 Read
6 Pumping System Understanding of Pump Head Read
7 Chilled Water Pump and Condenser Water Pump Power Pumping Power Calculation Read
   

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