1-     What is the concept of pressure drop?


There are two types of pressure drops, one is due to change in elevation and the other is due to resistance of pipe against the flow of fluid.

·       When a fluid in a pipe changes its elevation, it pressure will change.

·       When a fluid flows through a pipe regardless of elevation, it has to face the resistance and friction of the pipe. This resistance causes the loss of pressure of the fluid.


2-     How can we calculate the pressure drop caused by elevation change?


It is so simple!

For example: for water @

g: gravitational acceleration,

: difference in elevation m or ft

Example: A fluid in a 10 m vertical pipe flows up, what is the pressure drop caused by elevation?


3-     Can this App calculate the pressure drop caused by elevation change?


Unfortunately no, but anyway it is so simple and explained in 2th question.


4-     How can we calculate the pressure drop caused by flow through pipe?


Pressure drop in pipes caused by friction often calls Head Loss and the unit is the same as length.

f: friction factor

L: length of pipe

D: pipe diameter

V: fluid velocity

g: gravitational acceleration

For converting the Head Loss to pressure drop:


5-     Why “Head Loss” in the App introduced by the unit of   ?


“Head Loss” is often used in engineering text books as per unit length of pipe. For example if the “Head Loss” calculated   , it means every 100 ft of pipe will have 6 ft of head loss. So for the real head loss just do the math!


6-     How can we calculate head loss of water @ 45 flowing in 1” steel SCH40 pipe at the rate of 10 gpm in ?


By just selecting the “Pressure drop” and set the wheels as this figure, the head loss will be  . Also it calculated the velocity as .




This application calculates head loss per unit of length as pressure drop, just like many textbooks.


7-     How can we calculate the proper size of a pipe by just knowing the flow rate?


There are two pipe size criteria, head loss limit and velocity limit.

·       “Head loss limit method” mostly recommended for pipe sizing in close circuits, for example building hydronic system. In general it is recommended to size the pipe in HVAC systems with head loss limit between 2.5 to .

·       “Velocity limit method” is often used in pipe sizing for open circuits such as domestic water systems or irrigation systems. The most important issue in velocity limit is erosion of pipe. In general it is recommended the velocity between  to . The limits can vary according to the local codes and standards and also recommendation of pipe manufacturer.


8-     The flow rate for a hydronic system is 20 gpm, how can we calculate the size of steel pipe SCH80 at  ?


First “Pipe size head loss” must be selected, then set wheels of “Fluid type”, “Pipe Material”, “Pipe type” and finally set “Head Loss” for .

According to the figure, 1 ¼” can conduct up to 13.46 gpm @  head loss limit and 1 ½” can conduct 20.58 gpm @  head loss limit. So the answer is 1 ½”.



9-     How can we size a Polyethylene PN10 pipe for water temperature at  and flow rate of 30 gpm based on velocity limit method?


As shown in the figure, 50 mm can only conduct up to 25 gpm @  limit and 63 mm can conduct up to 39.94 gpm @  limit. So the answer is 63 mm.



10-  I need to calculate the pressure drop of a 40 mm Pex-Al-Pex pipe for 21.5 gpm @ . What can I do?


You cannot do it at  mode, because you cannot enter any fractional number there. For this situation we designed .



11-  I want to size a water SCH80 steel pipe @ for flow rate of 150 gpm, and I do not like the wheel type user interface, what can I do?


In this case you should use our mode. You will have 2 sizes then to choose in between. For 3 ½” the head loss is  and for 3” it is , So the answer is 3½”.