Mechanical Engineering - Hydraulics and Fluid Mechanics - Discussion

Gauge pressure = Pabs\Patm.
Vacuum pressure = Patm\Pabs.
Absolute pressure = Patm+Pgage.

Where- abs: absolute pressure.

Atm: Atmospheric pressure.

Gage: Gauge pressure.

Absolute pressure is measured relative to absolute zero on the pressure scale, which is a perfect vacuum. (Absolute pressure can never be negative). Absolute pressure is indicated by p, and is identical to the familiar thermodynamic pressure.

Gage pressure (sometimes written as "gauge pressure") is measured relative to the local atmospheric pressure. Gage pressure is thus zero when the pressure is the same as atmospheric pressure. (It is possible to have negative gage pressure).

Gage pressure is indicated by pg, and is related to absolute pressure as follows: pg = p-pa, where pa is the local atmospheric pressure.

1. Suction pressure: it's always negative in all pumps, here suction means to create vacuum for sucking the fluids from source area,

2. Vacuum pressure: it means below the atmospheric pressure,

3. Negative Gauge Pressure: it means pressure having a negative sign, so it's clearly known as less than the atmospheric pressure.

So from above notation answer D is Correct.

@Prabha.

It is not necessary to be suction pressure is only -ve pressure in case of the pump if pump discharge pr is very high about 200 300 kg etc then suction pressure is + ve also.

As we know that gauge pressure can be measured the atmospheric press. If pressure measured above the atmospheric pressure it is known as positive gauge pressure answer vice versa.

Why pressure gauge has 9 scale spacing at first part? Mine is (0-10) = 9 spacing (10-20) = 10 spacing unit psi.

@Dn Bhaskar.

How it will possible to suck the fluid at above atmospheric pressure?

Any body can explain suction pressure & negative gauge pressure?

Suction pressure can be positive also as in case of boiler feed pp.

Can you explain all type of pressures?

Nice solution @Radha.