Which statement about pressure units used in hydraulics is accurate?

Which statement about pressure units used in hydraulics is accurate?

• A. Psi
• B. PSIA
• C. Psig
• D. All of the above

Answer: (D)

Pounds per square inch is the common unit for hydraulic pressure, but you must know what reference point you’re using. The same psi unit can be used for different references: psig for gauge pressure, which is pressure above atmospheric pressure; and PSIA (or psia) for absolute pressure, which is pressure above a perfect vacuum. Since both forms express pressure in the same unit (psi) but with different references, they’re both valid in hydraulics depending on the context. For example, a system at 1000 psig has an absolute pressure of about 1014.7 psia at sea level, because atmospheric pressure is roughly 14.7 psi. This shows that the unit itself is versatile and can be used with either reference, so all of the forms mentioned are correct in the proper context.

Pounds per square inch is the common unit for hydraulic pressure, but you must know what reference point you’re using. The same psi unit can be used for different references: psig for gauge pressure, which is pressure above atmospheric pressure; and PSIA (or psia) for absolute pressure, which is pressure above a perfect vacuum. Since both forms express pressure in the same unit (psi) but with different references, they’re both valid in hydraulics depending on the context. For example, a system at 1000 psig has an absolute pressure of about 1014.7 psia at sea level, because atmospheric pressure is roughly 14.7 psi. This shows that the unit itself is versatile and can be used with either reference, so all of the forms mentioned are correct in the proper context.