pipers whenever any line is routed to feedwater tank it is connected to feedwater tank mostly with an orifice as a…

skgarg,
You wrote:
"Whenever a line is routed to a feed water tank, it is connected to feed water tank mostly with an orifice as a nozzle connection."
This does not make sense to me. Can you paste a part of the P&ID to this posting so we can see what you are talking about?

You asked a number of questions but without more information we cannot be of much help.
What is its reason?
No reason that I can think of.

Is the FLOW MEASUREMENT is the only reason?
Flow Measurement is the only reason for an Orifice run, however it would not be right at the nozzle.

What could be another reason?
None.

What is the pressure usually we maintain in Feed Water Tank?
It could be anything from Atmosphere to some medium to high pressure depending on the type of plsnt and the purpose for the feed water.

Hi JOP
i am attaching a snap shot of P&I which depicts the question i have asked in previous post.
hope now you will understand what i mean .
Regards
SG

You did not read the notes beside the lines.

They say "MinFlow Bypass" these are the minimum flow bypass lines on the Boiler Feed Pumps. These are not Flow measurement orifices sets. These are Flow Restriction Orifices. These have no instrument connections connected to them. They are just a blockage (plate) in the line with a predetermined sized hole in it. These normally do not require any specific upstream or downstream run distances.

Hi Jop
ya the four of them is minimum flow by pass line not the other one (preheating water return line)
anyway the question is this why we are using orifice plate or better say a plate with a hole .
obviously orifice plate is nothing but a pressure reducing component .
why we are reducing the pressure ...that is why i asked the question " what pressure is maintained in FWT"
is this vacuum we maintain in FWT ?
Regards
SG

Hi Jop
ya the four of them is minimum flow by pass line not the other one (preheating water return line)
anyway the question is this why we are using orifice plate or better say a plate with a hole .
obviously orifice plate is nothing but a pressure reducing component .
why we are reducing the pressure ...that is why i asked the question " what pressure is maintained in FWT"
is this vacuum we maintain in FWT ?
Regards
SG

A restriction Orifice does not reduce or restrict Pressure. It restricts Flow.

Hi,

There was an old thread which probably had similar discussion.

http://pipingdesigners.com/wp//phpBB3/viewtopic.php?f=1&t=2082&hilit=minimum+flow

Regards,

Flow transmitter (Flow Element) and Restriction Orifice are essentially thin plates installed.

1. If there's FE installed with instrumentation signal (FT) atop it which is sending the signal to some controlling element then it is for flow measurement.

2. In rest of the cases, restriction orifice works as flow reducer. Yes there will be pressure lost at orifice. Every piping commodity including pipe itself reduces pressure as fluid flows along (frictional losses). Even valves throttle as they are reduced bore. So that is why you'll see full bore / full port requirement for them as well, where necessary.

What you have stated below is fairly true. There's a point where the fluid cross-section is minimum (at the middle of the orifice plate) where the velocity will be maximum and pressure will be minimum. This is akin to Vena Contracta in a Venturimeter. This simply follows Bernoulli's equation. So across the Orifice what you have is increased velocity and reduced pressure. However, the volumetric flow rate remains constant.