What is the k-factor of a sprinkler

09/01/2023

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Currently, automatic sprinkler nozzles are designed according to certain standards. Customers when using sprinkler heads for fire fighting systems at construction sites will ask what is the k-factor of the sprinkler?

Dong Nam Company would like to introduce to our readers as follows:

1. K-Factor formula for sprinkler fire sprinklers. In this article, engineers consider the flow of water through a hole and will define the hole as an opening (with a closed circumference) in an element of the flow system. For this hole which will be a fire sprinkler or sprinkler in a fire protection system, we can use the k-factor formula for almost any circular hole. In 1644, an Italian physicist Torricelli (a student of Galileo and also inventor of the barometer) discovered that the flow although a hole transforms into the origin of pressure and then determined the relationship between the following basic relationships:

Q = AV

when:

Q = flow from hole

A =cross-sectional area of the hole

V = speed

This should lead to the accepted theorem for flow through a circular hole:

Q = A√ (2gh)

The above formula is theoretical and once we take into account the effects of friction, turbulence and contraction of the water flow, the formula can be simplified to the k-factor formula for fire protection systems. burn by reducing its complexity to a constant ''k''.

Formula K factor for fire prevention

When we start any hydraulic calculation for water based fire protection systems such as sprinklers, misting systems, the k-factor formula is the first formula that we will need to use. and since it's so basic, all fire engineers should have an understanding of how it works. In its most common form, the formula allows us to calculate the discharge flow from the nozzle (sprinkler, sprinkler or nozzle) if we get the head pressure and the factor k we can also calculate the factor k or the pressure required with this formula.

The discharge from the sprinkler or sprinkler can be calculated from the following formula:

q = kp 0,5

when:

q = flow

k =faucet discharge coefficient or k-factor for the head  p = Pressure

We can rewrite the formula to give us the coefficient k as follows:

k = q / p 0,5

or pressure as below:

p = (q / k) 2

The units the engineer uses are important and many should not be mixed. you also have to be very careful with the k factor and make sure you get the correct value for a metric or imperial calculation, the units for both are given below:

For data calculation:

p = internal pressure Bar

q = flow in liters per minute

k =discharge constant Lpm / Bar 0.5

and to calculate empire:

p = áp suất trong psi

q = lưu lượng trong gpm

k = hằng số xả gpm / psi 0,5 

We can also use K-factors for many other applications in fire hydraulics such as flow from a fire hydrant, wet outlet, spool or foam screen. In fact, the list is almost endless and this is why it is important to be familiar with the above formulas. Usually the K-factor is given an imperial value in gpm / psi ½ This value cannot be entered into the FHC without converting to the metric equivalent LPM / bar ½ . To convert gpm/psi½ to LPM/bar ½ we need to multiply by 14.4 (approximately) Example: A sprinkler head has a discharge coefficient of 4.2 gpm/psi ½ its metric equivalent valve is what. 4.2 x 14.4 = 60.48 LPM/bar ½ We just need to use K-factor to one decimal place to become 60.48 60.5 LPM/bar½

2. What is the k-factor value of the sprinkler head? Typical for sprinklers and misters

For a wide variety of standard nozzles, design standards such as EN 12845 & NFPA 13 specify standard k-factors and minimum pressures that should be used for different hazard classifications and design densities. . For all other types of sprinklers, the manufacturer's data sheet should be called for k-factor and minimum head pressure.

Nhóm sự cốMật độ thiết kế (mm / phút)Yếu tố KÁp suất tối thiểu (Bar)
Nguy hiểm ánh sáng2,25570,70
Nguy hiểm thông thường5,00800,50

As a designer, you must check the k-factor value for the nozzle or tip manufacturer and make sure its application is correct. You should also seek guidance from the applicable design standard.

3. Relationship between factor k, pressure and flow

The graph below shows the relationship between factor k, pressure and flow. You can clearly see this with the same pressure as with a high k-factor faucet, the flow from the tip or nozzle increases. We can sometimes use this to our advantage by choosing the correct sprinkler k-factor to provide the required design density with minimal energy requirements (water pressure).

Hệ số k của đầu phun sprinkler là gì?

 

For example if we have a pressure of 1.50 Bar and a k-factor of 50 then the flow rate will be 61.20 L/min for a k-factor of 100 it will be 122.50 L/min and with k factor is 150, the flow rate will be 183.70 L/min. You can see that the flow is unsafe about 61 L/min each time we change the k factor by 50, this is because the pressure stays the same at 1.50 Bar and if you look at the system formula the k on the pressure as squared will give us 1,225, which is then multiplied by the first k factor in this case 50, 100 and 150 in the example. As the k-factor increases by 50 each time, the increased traffic also increases by the same amount each time.

If you liked this article we try to help you also understand what is the k-factor of sprinkler heads?

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