Pressure Clarification

Back pressure and pressure drop mean the same thing....interchangable

Dear Mikerho...

Thanks for the explanation. Few queries with respect to the same:

1- With respect to concept of pressure drop: Pls clarify if orientation/position of pipe as (vertical or horizontal) also effects the pressure drop or Length of pipe alone takes care of this vertical/horizontal position of pipe.

2- With respect to concept of back pressure: Pls define back pressure more clearly...From this concept it seems that Back pressure is the P upstream of P Regulator only. What does the word back signifies?

1 - If flow is up, then gravity must be taken into account. There is a lot you can and should learn on line. Type "Fluid dynamics" into Google or other search engine. You should find the Wiki article thereof.

2 - The word "back", in this instance, is most closely defined as "before", which is the upstream pressure. In the case that R1 is a regulator, the back pressure will remain constant. If you replace R1 with a valve, the back pressure will not necessarily remain constant. You will always have a pressure drop which is equal to upstream pressure minus downstream pressure.

Start studying here:

http://en.wikipedia.org/wiki/Fluid_dynamics

Lots to learn, yes? Get busy!

Pressure drop is clear: it is the difference in pressure between the inlet and outlet sides of a device (a length of pipe, an orifice, a motor, a valve, etc.).

Back pressure is less clear -- or at least not consistently used.* Back pressure is the pressure on the outlet side of a device, and effects the performance of the device itself. Sometimes, the back pressure is regulated to achieve the desired device performance. A hydraulic motor, for example, will not move if the "front" (inlet) pressure and back (outlet) pressure are equal: there must be a pressure differential to create torque. Therefore, a valve in the return line of a hydraulic motor can both slow the motor and reduce its torque.

In practice, long return lines, clogged return line filters, etc, can cause enough back pressure to adversely affect the performance of the device in question.

Every device has a back pressure and a front pressure, and when there are a series of devices (as there almost always are) the back pressure for one device is the front pressure for the next in line (considering the lines themselves as "devices").

* Here is a thread in which there is not a lot of agreement.

The term "back pressure" is ambiguous, and hence can be confusing. Mikerho and K Fry are both correct, but in different contexts.

Consider it like this - 2 pumps compressors operating at the same time and delivering air into a central pipe. one can develop problem and there will be a pressure drop but immediately there will a back pressure from the other working perfect. Hence, recommended non return/check valve on each to safeguard damage against back pressure. Now similar with 2 boilers/pumps.

There is a process filter and a PSV(press. safety valve) downstream of it. PSV is located at a height H from filter and connected by piping.

The supplier of this filter and PSV has asked us to provide back pressure on/due to PSV to calculate the size for the same. How this value is established and how sizing will be done based on this value?

Can you provide a schematic of the system?