Emergency Pressure Vent Cover NK-EV31W

API Standard 2000 for Venting / Atmospheric and Low Pressure storage Tanks / SIZING A PRESSURE/VACUUM RELIEF VALVE
API standards are provided as an engineering aid for specification and selection of “normal” and “emergency” pressure and vacuum relief valves for aboveground liquid petroleum storage tanks. Normal venting capacity is obtained without exceeding pressure or vacuum that would cause physical damage or permanent deformation to the tank. The following will help in sizing a pressure/vacuum valve:
1. NORMAL RELIEF : the sum of vapor replacement resulting from emptying or filling and thermal in-breathing or out-breathing.
2. EMERGENCY RELIEF : thermal out-breathing from fire exposure.
3. ALL TANKS : generally require the sizing of a normal pressure and vacuum relief valve to be sized and an independent emergency relief valve to be sized separately.
4. FLOW CURVES : these curves provide pressure and vacuum capacity which is required for sizing.

MODEL NAME : NK-EV31W

NK-EV31W PHOTO

NK-EV31W PHOTO

DESIGN AND FUNCTION

Model No.

Type Material

Setting Pressure Range

NK-EV31W

Weight Loaded release to ATM Aluminum, Carbon Steel, Stainless Steel

22 ~ 700 mmH2O

NK-EV31S

Spring Loaded to ATM Aluminum, Carbon Steel, Stainless Steel

Above 700 mmH2O

Note) Other specification to be consult by factory.

Model NK-EV31 SERIES is designed to protect the tank against rupture or explosion that could result from excessive internal pressures caused by fire etc. Model NK-EV31 SERIESis designed to provide emergency relief capacity beyond that furnished by the normal operating pressure relief valve on the storage tank. The feature of Model NK-EV31 SERIES is that the pressure relief cover is designed to lift only far enough to flow its rated capacity should high tank pressure be encountered then reseal automatically when the tank pressure is reduced.

MATERIALS

PART NAME MATERIALS STANDARD MATERIALS OPTIONAL
BODY C.S / SUS304 / SUS316 / ALUMINUM Hastelloy, Alloy 20, FRP, PTFE, ETFE LINED
PALLET 304 SS / 316 SS / 316L SS Hastelloy, Alloy 20, FRP, PTFE, ETFE LINED
WEIGHT A36 304 S.S
DIAPHRAGM/ORING Teflon(Diaphragm seal) NBR, Viton(O-ring seal)

PRESSURE/VACUUM RELIEF VALVE SETTING
API 2521
Pressure/vacuum valves on atmospheric pressure fixed roof tanks are usually set at 1/2 oz. per square inch pressure or vacuum. Test data indicate that an increase of 1 oz. per square inch in the pressure set point over the usual 1/2oz. per square inch reduces breathing losses by approximately 7 percent. However, the test data indicate that each additional increase of 1 oz. per square inch in pressure set point reduces the breathing losses in progressively smaller increments.

API 2513
The pressure and vacuum setting of a breather valve are dictated by the structural characteristics of the tank and should be within safe operating limits. A certain amount of pressure and vacuum beyond this setting is necessary to overcome pressure drop in order to obtain required flow. Proper size and setting can best be determined by reference to API STD accordance with this publication. The pressure setting for pressure/vacuum valves to be installed on large tanks constructed in accordance with API 12:Specification for Large Welded Production Tanks(1957)usually is limited to 1/2 oz. because roof plates will start to shift when the pressure rises much above 1 oz.

Pressure Relief
As the pressure in the storage tank increases, when the set pressure is reached, the pressure pallet lifts and relieves to atmosphere.

Vacuum Relief
As a vacuum is drawn in the storage tank (for example, when fluid is being pumped out), the pressure pallet is held shut by atmospheric pressure. When the vacuum setting is reached, the pallet lifts and air is drawn in the storage tank from the atmosphere.

MODEL NAME : NK-EV31W PRESSURE

MODEL NAME : NK-EV31W VACUUM

MODEL NAME : NK-EV31S PRESSURE

MODEL NAME : NK-EV31S VACUUM

DRAWING AND DIMENSION

SIZE I.D T H
16” 400 20 600
20” 500 20 700
24” 600 20 800

UNIT : mm