Pound # vs. PSI (UOM)

I am not too familiar with units; However, looks to me that they are differents animals.

PSI are units to be used in pressure and Poundals are used to indicated wheigts, therefore, looks that there are not relation betwen them.

Ansory if this will not hel you.

Best Regards

Pound is a measure of force or weight, PSI (pounds per square inch) is a measure of pressure or stress.

3000 psi= 300 pounds X 10 in^2

Hi Steve,

Correction!

3000 psi = 3000 lb / 1 in² or 30000 lb / 10 in²

or maybe what you were trying to say was:

3000 lb = 300 psi x 10 in²

Mike

Right Mike, I messed up the math. Writing too fast. Sorry.

3000 psi= 3000 lb/1 in2

Maybe a practical example will help. Suppose you have a 2-inch diameter hydraulic cylinder operating at 3000 psi (pounds per square inch). The area of this cylinder is π in² ≈ 3.1416 in². Thus 3000 psi x 3.1416 in² ≈ 9424.8 pounds of force exerted by the cylinder.

Force is just force; pressure or stress is force per area (force ÷ area). Or, rearranging terms, force = pressure (or stress) × area.

These both units of measurement are the same applied to Oil & Gas projects. Pound, as # symbol is just an abbreviation of unit, (psi); One best example, in Flange rating, like we commonly call-out as 150# rating, or ASME Class 150# rating are not acceptable. The right word to say is ASME Class 150, 300, 600, 900, 1500, 2500 belongs to ASME Code. While 3000, 5000, 6000, 10,000, 15,000 psi belong to API Code. There it is acceptable to say 3000#, or 3000psi. The unit for pressure rating, like for wellheads are express in PSI as #, and unit for pressure for flange rating is ASME Class 150, 300, 600..so on and so forth. I hope above clarifies your doubts.

In FPS (Foot, Pound Second) system of units (Now a days we mainly use SI system of units) pound is the unit of weight, force and PSI (Pounds per square inch) is the unit of pressure. Pressure is defined as force per unit area i.e. pounds per square inch. For example atmosphere pressure is 14.7 PSI at sea level which means every square inch of land, sea, person or article bears a weight or force of 14.7 pounds.

You've been talking to, or reading articles by lazy Americans, haven't you. We have a bad habit of dropping what we consider excess baggage (per square inch) if we assume the party on the other end of the conversation knows what we are talking about. We do it so often, it ends up in technical articles at times, where the full unit of measure should always be reported.

We'll just say revs for revolutions per minute, inches for inches of mercury or inches of water, if we figure that everyone knows which we mean, and so on.

I was also confused by the OP, since they are different units as many posts have explained.

But PHYS got it right--the OP has run into someone using notation shortcuts which cause huge confusion when taken literally.

Pound or pounds is a measurement of weight, such as one gallon of water weighs 8.33 LBS. (pounds)

PSI is the measurement of pressure (pounds per square inch)

This can be produced several different ways, foe example a pump can produce pressure to cause a liquid to move through a piping system to extreme heights, a pressure gauge will be installed to confirm what the pressure is in the system.

In hydraulics you can use this pressure in a hydraulic piston to move an object that is very heavy, example 100 PSI (pounds per square inch) multiply this by the area of the piston in the cylinder (square inches) this will result in the force generated against the piston to move the heavy object. pressure x area = force

This is very basic I hope this explanatrion helps

While I work in the compressor industry, I use PSI whenever I am writing reports, invoices, technical papers, etc. to my customers or supervisors. When I am making notes to myself I will use the # symbol as a simple way to describe pounds per square inch. In other words, PSI is the correct way to describe pounds per square inch. However, there is also PSIG (gauge pressure) and PSIA (absolute pressure). WE use normally use PSIG to describe the pressure we are working with. PSIA--absolute pressure is gauge pressure--that seen on the gauge --plus atmospheric pressure added together.

lb = Mass

lbf = Force

PSI = Presure

PSI = lbs/inch2

3000 PSI = 3000/1in2

Hi zubaidi,

Let us assume you have a large feline which you suspend from a spring balance and he/she weighs 15 pounds. That is weight. You then sit the same feline atop a frictionless plunger mechanism which communicates that weight to a fluid, if the effective surface area of that mechanism is 1square inch you (it) will generate an hydraulic force of 15psi(g). Note the last letter as this defines the pressure above atmosphere as against absolute.

First find a substantial feline (or equivalent mass) to start this experiment.

Enjoy experimenting.

Massey.

Suppose 3000 psi =?#(pound)

PSI is a unit for measuring a pressure ( pressure is a Force per Unit Area), where

# is just a symbol for Rating or Class of such a fitting or a flange.

For more information, see the following CR4 Threads:

• Pound Rating

• Pressure Rating

• Piping Standards and Fittings

• Rating of Pipe Fittings