Pump Head တြက္နည္း ( အဲယားကြန္း ပညာ )

Pump Head Calculation

Pump head is a measure of energy. The units of energy are expressed in feet or meters. Pump head သည္ စြမ္းအင္ ေပ သုိ့ မီတာ (feet or meters)ကိုေဖာ္ၿပသည့္ နည္းတစ္မ်ိဳးၿဖစ္သည္။

ဖိအားဆုိသည္မွာ a unit of area အေပၚသို့ သက္ေရာက္ေနေသာ အားပမာဏတစ္ခုၿဖစ္သည္။ ၁ ေပါင္ အားပမာဏ သည္ တစ္လက္မပတ္လည္ ဧရိယာေပၚတြင္သက္ေနေရာက္ေနလွ်င္ ဖိအား a square inch of area, or PSI ဟုေခၚသည္။ အရပ္သံုးစကားအရ "ေလေပါင္တစ္ေပါင္" အားဟုေၿပာဆုိေလ့ရွိသည္။

သိုေသာ္ 1 PSI ကို (ft of water) ႏွင့္ေဖာ္ၿပမည္ ဆုိလွ်င္ Head (ft. of water)/2.31 = PSI and PSI x 2.31 = Head (feet of water)

pumps မ်ားအတြက္ , 70 feet of head ကို ပို့ေပးနိင္သည့္ Pump သည္ 30 PSI of differential pressure across the pump (i.e., 70 feet/2.31 = 30 PSI.)

pump manufacturer မ်ားသည္ တစ္ညီတညြတ္တည္း “head” သည္ ေဝါဟာရကို အသံုးၿပဳၾကသည္။ Pressure ဟုေၿပာဆုိလွ်င္ pump မွတြန္းနုိင္ေသာ Pressure သည္ တြန္းပို့မည့္ liquid ၏ the weight (specific gravity) ႏွင့္ the specific gravity changes with temperature, fluid အမ်ိဳးအစားႏွင့္ and fluid concentration တုိ့ေပၚတြင္မူတည္သည္။

“head” မ်ားကို တိုင္းတာသည့္ အခါ the center line of the pump မွ တဆင့္ the highest liquid level အထိတိုင္းတာေလ့ရွိသည္။

pump၏ suction ဘက္ႏွင့္ discharge ဘက္တုိ့

resistance in the piping, fittings and valves တိုေၾကာင့္ၿဖစ္ေပၚလာေသာ Head ကို friction head ဟုေခၚသည္။ any pressure that might be acting on the liquid in the tanks including atmospheric pressure ကို " surface pressure head"ဟုေခၚသည္။

the Static discharge head ထဲမွ the Static suction head ကို ႏွတ္လွ်င္ Static Head ကို ရသည္။

System head = total discharge head - total suction head ( တစ္ခါတစ္ရံ Static ဆိုသည့္ စကားလံုးကို friction head မပါဝင္ပါ ဟုသိသာေစရန္ ထည့္သံုးသည္။)

H = hd - hs

The total discharge head is made from three separate heads:

hd = hsd + hpd + hfd

• hd = total discharge head
• hsd = discharge static head (discharge ဘက္တြင္ရွိေသာ Elevation ေၾကာင့္ၿဖစ္သည့္ static head)
• hpd = discharge surface pressure head ( Open System မ်ားတြင္ atmospheric pressure ကို ဆုိလိုသည္။)
• hfd = discharge friction head ( fluid စီးဆင္းမွဳေၾကာင့္ၿဖစ္ေပၚလာေသာ Pressure losses မ်ား)

The total suction head also consists of three separate heads

hs = hss + hps - hfs

• hs = total suction head
• hss = suction static head (suction ဘက္တြင္ရွိေသာ Elevation ေၾကာင့္ၿဖစ္သည့္ static head)
• hps = suction surface pressure head ( Open System မ်ားတြင္ atmospheric pressure ကို ဆုိလိုသည္။)
• hfs = suction friction head ( fluid စီးဆင္းမွဳေၾကာင့္ၿဖစ္ေပၚလာေသာ Pressure losses မ်ား)

"feet of liquid gauge" သို့မဟုတ္ "feet of liquid absolute" ယူနစ္မ်ား အတုိင္း တြက္ခ်က္မွဳမ်ားၿပဳလုပ္နုိင္သည္။ . "absolute ဆုိသည္မွာ the gauge reading တြင္ atmospheric pressure (head) ကို ထည့္ေပါင္းထားၿခင္းၿဖစ္သည္။

ဤဥပမာသည္ Opened System ၿဖစ္သည္။ ACMV system မ်ားတြင္ Cooling Tower သို့ Condenser Water pump ကို တြကပံုမ်ိဳႏွင့္ဆင္တူသည္။ ဤဥပမာ တြင္ The suction head သည္ အႏွဳတ္ (negative) တန္ဘုိးၿဖစ္ၿပီး Condenser Water pump တြင္ The suction head သည္ အေပါင္းတန္ဘိုးၿဖစ္သည္။

Begin with the total suction head calculation

1. The suction head သည္ အႏွဳတ္ (negative) တန္ဘုိးၿဖစ္သည္။ The liquid level in the suction tank ၏ the liquid level သည္ the centerline of the pump ထက္နိမ့္ေနသည္။

hss = - 6 feet ( ပန့္တည္ရွိသည့္ေနရာကို Elevation = 0 ft ဟုယူ၍တြက္ခ်က္ေသာေၾကာင့္ ၿဖစ္သည္။ အႏွဳတ္ သေကၤတမွ စုပ္ယူရမည့္ Fluid ၏ Elevation သည္ Pump ထက္ ၆ေပနိမ့္သည့္ေနရာတြင္ရွိသည့္ဟုဆုိလိုသည္။ )

2. The suction tank သည္ အပြင့္ ပံုစံၿဖစ္သည္ (Open) , ထုိေၾကာင့္ the suction surface pressure သည္ atmospheric pressure ႏွင့္ ညီသည္။

hps = 0 feet gauge ( atmospheric pressure သည္ suction ဘက္ႏွင့္ discharge ဘက္တြင္ မွာပါ သက္ေရာက္ေနသည္။ထိုေၾကာင့္ မည့္သည့္တန္ဘိုးထည္တြက္သည္ၿဖစ္ေစ ေက်သြားလိမ့္မည္။)

3. the suction friction head တြက္ယူရန္, (ဤစာမ်က္ႏွာတြင္ the suction friction head ကို မည့္သို့တြက္ခ်က္သည္ မေဖာ္ၿပပါ။ 4 feet ဟုယူဆ၍တြက္သည္။)

hfs = 4 feet at rated flow ( friction loss calculation မွ ရရွိသည္။ friction loss calculation တြက္နည္းကို ေနာက္ စာမ်က္ႏွာမ်ားတြင္ေဖာ္ၿပမည္)

4. The total suction head သည္ a gauge တန္ဘိုးၿဖစ္သည္။ အဘယ္ေၾကာင့္ဆုိေသာ္atmosphere Pressuer ကို 0 အၿဖစ္တြက္ခ်က္ေသာေၾကာင့္ၿဖစ္သည္။

hs = hss + hps - hfs = -6 + 0 - 4 = -10 feet of liquid gauge at rated flow

The total discharge head calculation

1. The static discharge head is:

hsd = 125 feet ( ပန့္တည္ရွိသည့္ေနရာကို Elevation = 0 ft ဟုယူ၍တြက္ခ်က္ေသာေၾကာင့္ ၿဖစ္သည္။)

2. The discharge tank သည္ အပြင့္ ပံုစံၿဖစ္သည္ (Open) , ထုိေၾကာင့္ the suction surface pressure သည္ atmospheric pressure ႏွင့္ ညီသည္။

hpd = 0 feet, gauge

3. The discharge friction head ကို ၂၅ feet ဟုယူဆ၍တြက္သည္။discharge friction head သည္ pipe အတြင္းတြင္ရွိေသာ Fluid Velocity ႏွင့္ Fitting အေရအတြက္တို့ေပၚတြင္မူတည္သည္။

hfd = 25 feet at rated flow

4. The total discharge head is:

hd = hsd + hpd + hfd = 125 + 0 + 25 = 150 feet of liquid gauge at rated flow

The total system head calculation:

H = hd - hs = 150 - (-10)= 160 feet of liquid at rated flow

Note: did you notice that when we subtracted a minus number (-10) from a positive number (150) we ended up with a positive 160.

chart section

vacuum application ႏွင့္သက္ဆုိင္ေသာ ဥပမာ ကို ဆက္လက္တြက္ခ်က္ပါမည္။ . Pipe friction တန္ဘိုးမ်ားကို Hydraulic Institute Engineering Data Book မွ ရယူရန္ၿဖစ္သည္။ chart section

Specifications:

1. Transferring 1000 gpm. weak acid from the vacuum receiver to the storage tank. အက္စစ္ေပ်ာ့မ်ားထည့္ထားသည္ အလံုပိတ္ကန္မွ တစ္မီနစ္လွ်င္ အက္စစ္ ဂါလံ 1000 တြန္းပို့ရန္ၿဖစ္သည္။

2. Specific Gravity - 0.98 (ထည့္ထားေသာ အက္စစ္ ၏ သိပ္သည္းဆ Specific Gravity မွ 0.98 ၿဖစ္သည္။)

3. Viscosity - equal to water (ပ်စ္ေစးမွဳ Viscosity သည္ ေရ၏ ပ်စ္ေစးမွဳ Viscosity ႏွင့္တူညီသည္။)

4. Piping - All 6" Schedule 40 steel pipe - ပိုက္အမ်ိဳးအစားမ်ားမွာ Schedule 40 အဆင့္ရွိေသာ steel pipe မ်ားၿဖစ္သည္။

5. Discharge piping rises 40 feet vertically above the pump centerline and then runs 400 feet horizontally. There is one 90° flanged elbow in this line.

Dischargeပိုက္သည္ ပန့္ႏွင့္ေမာ္တာ မွ အထက္ ေပ ၄၀ အၿမင့္တြင္ရွိသည္။ ထုိေနာက္ ေလွာင္ကန္သို့ေရာက္ရန္ ေရၿပင္ညီအတုိင္း ေပ 400 အရွည္ရွိသည္။ 90° flanged elbow တပ္ဆင္ထားသည္။

6. Suction piping has a square edge inlet, four feet of pipe, one gate valve, and one 90° flanged elbow all of which are 6" in diameter.

Suction ပိုက္တြင္ a square edge inlet, four feet of pipe, one gate valve, ႏွင့္ one 90° flanged elbowတပ္ဆင္ထားၿပီး ပိုက္ diameter မွာ ၆ လက္မၿဖစ္သည္။

7.The minimum level in the vacuum receiver မွာ the pump centerlineထက္ ၅ ေပၿမင့္သည္။

8. Vacuum ေလွာင္ကန္ထဲတြင္ရွိေသာ pressure မွာ 20 inches of mercury, vacuum ၿဖစ္သည္။

To calculate suction surface pressure use one of the following formulas:

• inches of mercury x 1.133/ specific gravity = feet of liquid
• pounds per square inch x 2.31/specific gravity = feet of liquid
• Millimeters of mercury / (22.4 x specific gravity) = feet of liquid

the system ကို pump ေနရာ မွ ႏွစ္ပုိင္း ပိုင္း၍ တြက္ခ်က္ပါမည္။

Total suction head calculation

1. The suction side of the system shows a minimum static head of 5 feet above suction centerline. Therefore, the static suction head is:

hss = 5 feet

2. Using the first conversion formula, the suction surface pressure is:

hps = -20 Hg x 1.133/ 0.98 = -23.12 feet gauge

3. The suction friction head, hfs, equals the sum of all the friction losses in the suction line. Friction loss in 6" pipe at 1000 gpm from table 15 of the Hydraulic Institute Engineering Data Book, is 6.17 feet per 100 feet of pipe.

in 4 feet of pipe friction loss = 4/100 x 6.17 = 0.3 feet

Friction loss coefficients (K factors) for the inlet, elbow and valve can be added together and multiplied by the velocity head:

FITTING	K	FROM TABLE
6" Square edge inlet	0.50	32 (a)
6" 90 flanged elbow	0.29	32 (a)
6" Gate valve	0.11	32 (b)

Total coefficient, K = 0.90

Total friction loss on the suction side is:

hfs = 0.3 + 1.7 = 2.0 feet at 1000 gpm.

4. The total suction head then becomes:

hs = hss + hps - hfs = 5 + (-23.12) - 2.0 = -20.12 feet, gauge at 1000 gpm.

Total discharge head calculation

1. Static discharge head = hsd = 40 feet

2. Discharge surface pressure = hpd = 0 feet gauge

3. Discharge friction head = hfd = sum of the following losses :

Friction loss in 6" pipe at 1000 gpm. from table 15, is 6.17 feet per hundred feet of pipe. In 440 feet of pipe the friction loss = 440/100 x 6.17 = 27.2 feet
Friction loss in 6" elbow:

from table 32 (a), K = 0,29

from table 15, V2/2g = 1.92 at 1000 gpm.

Friction loss = K V2/2g = 0.29 x 1.92 = 0.6 feet

The friction loss in the sudden enlargement at the end of the discharge line is called the exit loss. In systems of this type where the area of the discharge tank is very large in comparison to the area of the discharge pipe, the loss equals V2/2g, as shown in table 32 (b).

Friction loss at exit = V2/2g = 1.9 feet

The discharge friction head is the sum of the above losses, that is:

hfd = 27.2 + 0.6 + 1.9 = 29.7 feet at 1000 gpm.

4. The total discharge head then becomes:

hd = hsd + hpd + hfd = 40 + 0 + 29.7 = 69.7 feet, gauge at 1000 gpm.

c. Total system head calculation:

H = hd - hs = 69.7 - (-20.2) = 89.9 feet at 1000 gpm.