PRD (API 576)

Question 1

Weight-loaded Pressure-/Vacuum-relief Valve (3)

Answer 1

1. These devices are used where operating pressures are very near atmospheric conditions.
2. The set pressure or vacuum setting can be changed by adding or removing weights in the seating area of the valve.
3. They are often used to satisfy the normal venting requirements caused by thermal inbreathing/outbreathing and product pump-in/pump-out effects.

Question 2

Pressure- and/or vacuum-vent valves Designed to what?

Answer 2

designed to vent air and vapor from the tank during filling operations and to admit air when the tank is drawn.

Question 3

PVRV are prone to what?

Answer 3

sticking (Periodic examination may detect this condition. )

Question 4

Where temperatures fall below freezing, what to be done?

Answer 4

the devices may need to be checked during the cold period to ensure that the discs (normally called pallets) do not stick because of icing.

Question 5

Recommended steps for inspection (9)

Answer 5

1. The discs (normally called pallets) of the devices should be checked for sticking.
   2 .If the mass is not correct, mass should be added or removed until the correct mass has been achieved.
2. The seats and pallets should be checked and cleaned
3. The gaskets at the pallet seating areas should be checked and, if necessary, replaced
4. The protective screens should be checked for serviceability and, if necessary, renewed.
   6.If the weights are positioned on a moment arm attached to the seating area, then hinges and hinge pins should be checked for operability and, as necessary, serviced, lubricated, and replaced.
5. Any special coating used internally or externally on the body should be checked and, if unserviceable,
   replaced.
6. The hood should be inspected and, if unserviceable, replaced.
7. The bolts should be checked and, as required, replaced.