water pressure question, pls help

[mrvicz]

hello,

ive been trying to figure out my problem but couldnt find an answer. anyways, say that i have a 400gph pressure from a pump that throws water into a 3/4" hose ... at the other end of the hose, i use a reducer to output the water thru a 1/2" hose. now my question is, will there be a change in the water pressure?


input would be greatly appreciated. big thanks!

vic

 

[sowellj]

Very likely. You can think of it like this ... if you totally blocked the outlet pressure would increase. Reducing the output diameter will likely cause an increase in pressure at that flow.

 

[sarmo]

what size is the output from the pump? if you decrease the pipe diameter you are actually increasing the velocity of the water but the pressure is less, (assuming the same volume) it's a weird pressure, flow and volume relationship...

why do you ask?

 

[mrvicz]

im asking because from my pump, water goes to my manifold which feeds several reactors through a 3/4" hose, one of them is being stepped down to a 1/2" hose ... and flow needs to be max of 100gph. altho i have a flowmeter but it has been placed at the 3/4 hose.

TIA.

 

[wooden_reefer]

hello,

ive been trying to figure out my problem but couldnt find an answer. anyways, say that i have a 400gph pressure from a pump that throws water into a 3/4" hose ... at the other end of the hose, i use a reducer to output the water thru a 1/2" hose. now my question is, will there be a change in the water pressure?


input would be greatly appreciated. big thanks!

vic

The answer is yes.

First, 400 gph is not a pressure, it is a flow rate. The pump generates a force and hence pressure that when overcoming the friction and static pressure (head) produces this rated flow rate.

Energy is lost to overcome friction in a conduit or fitting, so with flow pressure is reduced as it is measured at the other end. The higher the flow the greater the energy loss and the greater the pressure drop.

The friction is greater with narrower conduit.

Say if the flow is very slow, there will not be much pressure drop from one end of a conduit to another.

 

[sarmo]

one thing is for sure, if you have a flow meter on the 3/4 inch and it says you are getting 100gph then you are also getting 100gph from the 1/2inch. assuming the two pipes are directly connected and there is no other place for the flow to go.

what goes thru the 3/4 has to be going through the 1/2 it's just going faster through the 1/2 inch.

wodden reefer- well said

 

[mrvicz]

Oh, ya, i shouldve meant flow rate and not pressure, very sorry for the confusion for the first ones to reply, my bad ... my question shouldve been; if there is a change in flow rate when water coming from 3/4" hose is reduced to 1/2", will there be a flow rate change at the 1/2" end.

The answer is yes.

First, 400 gph is not a pressure, it is a flow rate. The pump generates a force and hence pressure that when overcoming the friction and static pressure (head) produces this rated flow rate.

Energy is lost to overcome friction in a conduit or fitting, so with flow pressure is reduced as it is measured at the other end. The higher the flow the greater the energy loss and the greater the pressure drop.

The friction is greater with narrower conduit.

Say if the flow is very slow, there will not be much pressure drop from one end of a conduit to another.

 

[mrvicz]

now that is what i wanted to find out. thank you very much sarmo.

one thing is for sure, if you have a flow meter on the 3/4 inch and it says you are getting 100gph then you are also getting 100gph from the 1/2inch. assuming the two pipes are directly connected and there is no other place for the flow to go.

what goes thru the 3/4 has to be going through the 1/2 it's just going faster through the 1/2 inch.

wodden reefer- well said