plz help with fire pupm 1

[Almhmudi]

hi all
plz how could i calculate the head and pressure of fire pump if its location ware at the top of the building?
th u all

 

[LittleInch]

By designing it.

That's a strange position though.

Needs lots more details.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Is the tank on the roof?

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Almhmudi]

thank u for your respondes
the tank and the fire pump must be at the top roof , there is no space at the basement.
the fire stand pipe class 2 with 6 floors cabins are needeed ,
100 gpm and at lest 4.6 bar for pressure, 1.5" end hose ,
now what the diffrent in calculation if the tank and pump ware at the top roof vs if it ware at the basement?
thx all

 

[1503-44]

No difference. You just have to figure out how to get the water up to the roof, if street pressure isn't enough to do it alone. What's your minimum street pressure?

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Almhmudi]

I HAVE A WATER TANK OVER THE BUILDING FOR FIRE READY TO WORK
SO THERE ARE NO DIFFERENT IN PUMP PRESSURE AND PIPE SIZE IN BOTH CASE?

 

[LittleInch]

There is, but we have no data on fire pump position and where the floor is.

Send us a good cross sectional drawing of the building.

But the issue is how do you fill your water tank?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Almhmudi]

THNAK U VERY MUCH
I ATTACHED A (PDF) FILE SHOWING THE PLAN,
the cross section for the building

 

[LittleInch]

Almhmudi,

1, Please don't Use ALL CAPITALS - It's regarded as SHOUTING and is normally avoided unless for emphasis.
2) So I can only assume your fire water tank is on the top floor and you can get > 100 GPM into it using the water pressure from the street.
3) It looks like the vertical distance between pump and first hydrant is about 3.5m.
4) Distance to the lowest hydrant is

So to get your min pressure of 4.6 bar at the highest hydrant you need a pump capable of 100 GPM @ a differential head of about 43.

Note that the no flow head will be higher, so prob about 5.5 bar at the highest hydrant and 7.1 bar at the lowest hydrant.

Normally the pump would not be so big as the inlet pressure from the supply in the street is higher than the 0m I've allowed for.

Does that make sense?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Almhmudi]

thnk u my friend it is very helpfull

1- the fire water tank is on the top floor.
2- Distance to the lowest hydrant is 16.5m.
3- why ==> (a differential head of about 43).
4- (so prob about 5.5 bar at the highest hydrant and 7.1 bar at the lowest hydrant) what about the gravity?

grateful.

 

[LittleInch]

3) I assume the water level is the same as the pump inlet in the worst case (nearly empty). You need 46m head at the hydrant. The hydrant is 3m below the pump, so the pump only needs to do 43m differential head.

4) I've estimated that at no flow but with the pump on, the differential head would be about 52m. So then add on the head gain due to gravity and then you get 55m (5.5 bar) at the highest hydrant and 70m (7 bar) at the lowest hydrant.

Makes more sense now?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Almhmudi]

my friend why you add head (So then add on the head gain due to gravity and then you get 55m (5.5 bar) at the highest hydrant and 70m (7 bar) at the lowest hydrant.)
i thinked that i must subtract the head value becuse the pump is over the top roof and the gravity help it to reduce the pressure that it need to made the right flow?

 

[LittleInch]

You mis understand what I'm saying.

You need to have 4.6 bar at the highest hydrant. Then you add the gravity to this pressure to see if the pressure at the LOWEST hydrant is still acceptable.
Your pump doesn't know which hydrant is in operation
My point in item 4 is that if the pump is turned on with NO FLOW, then the pressure at the lowest hydrant will be about 7 bar, so your design and components need to allow for that.

My assumption is that you don't have any pressure control or pressure regulation and this a simple vertical pipe going down between the floors with a hydrant stuck on it.

does that help?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Almhmudi]

now that's is so logically .
really that's great you helped me so much thank you sir.

 

[Almhmudi]

one more question please,
how did you calculate the 5.5 bar at no flow case?

 

[LittleInch]

It was an estimate based on experience.

If you need a differential head of 43m,, for that size of pump a no flow diff head of 20% over "duty point" is possible, so 42 x 1.2 = ~52m, plus the 3m hed difference = 55m / 5.5. bar.

These are pretty small pumps so it's all a bit basic - you get what you buy, not always what you need, so always best to allow a bit more than the minimum

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Almhmudi]

nice
now would you mind if you tell me,
why the codes showing the no flow & shut off pressure are at 140% of the pump pressure , not 20%?
do i missing some thing?

 

[LittleInch]

If the codes say 140% then use 140% - they are just covering themselves as different pumps have different %. Most won't be as bad as that, but the odd one might be so they just take the worst case.

I just took 20% as a guess / estimate to illustrate a point.

Note, if this is under NFPA specs then follow them - they are a world different from most others and include things I wouldn't on a normal distribution system, but that's NFPA / fire systems for you.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Almhmudi]

really I cant express my grateful to you,
you helped me so much,
thank you my teacher