China DF-ISO Cast Steel High Velocity Pressure Vacuum Valve with Gas Freeing Cover:
High Velocity Pressure Vacuum Valve is called PV valve or P/V valve for short, generally used in the relief system of the oil tanker and chemical tanker, according to the current regulations IMO and IBC.
When the pressure in the tank reaches the set pressure of relief valve, the gas in the tank will be released with the speed of over 30m/s. The vacuum will beformed while the cargo oil tank is unloading, when the vacuum pressure reaches the set pressure of vacuum valve (normally it is -3.5Kpa), the vacuum valve will open automatically,then the air will go into the tank through the flame screen.
A manual ventilation device is necessary when other works that requires ventilation are being done in the cargo oil tank, such as cleaning, degassing...etc. At this time, the pressure in the tank is too low or without without pressure, the valve can not be opened. (The pressure valve is not manual and it will work with the velocity of smaller than 30m/s). The manual ventilation device is the gas freeing cover. It can prevent the flame into the tank. PV valve with gas freeing cover can breathe through opening the gas freeing cover even when the pressure valve or vacuum valve are faulty.
Gas Freeing Cover is comprised of upper cover, flame screen and shell, can be installed on the top of the vacuum valve.
Technical Specification:
1. Design Standard: ISO 15364-2007, MSC/circ. 677, GB/T19699-2012, MSC.1/circ. 1324, MSC/circ. 1009
2. Flange Standard: GB2506, JIS B2220, ANSI, DIN
3. Design Pressure:
Opening Pressure of Pressure valve: 14Kpa for Oil cargo tank, 20Kpa fo chemical cargo tank.
Opening pressure of Vacuum Valve: -3.5Kpa.
Certificate:
CCS, BV, ABS Type Approval Certificate and Product Certificate, NK product certificate
Main Parts and Material:
| Serial No. | Parts | Quantity | Material | Remarks |
| 1 | P-valve base | 1 | ZG200-400 | Cast 20# |
| 2 | Water nozzle | 1 | 0Cr18Ni9 | SUS304 |
| 3 | P-valve seat | 1 | 0Cr18Ni9 | SUS304 |
| 4 | P-valve disc | 1 | 0Cr18Ni9 | SUS304 |
| 5 | Matching block | 1 | 0Cr18Ni9 | SUS304 |
| 6 | P-valve body (A) (B) | 1 | ZG200-400 | Cast 20# |
| 7 | Conducting machine | 1 | 0Cr18Ni9 | SUS304 |
| 8 | Handle | 1 | 0Cr18Ni9 | SUS304 |
| 9 | V-valve body | 1 | ZG200-400 | Cast 20# |
| 10 | Matching block | 1 | 0Cr18Ni9 | SUS304 |
| 11 | V-valve disc | 1 | 0Cr18Ni9 | SUS304 |
| 12 | V-valve seat | 1 | 0Cr18Ni9 | SUS304 |
| 13 | Flame screen | 2 | 00Cr17Ni14Mo2 | SUS304 |
| 14 | Flame screen gland | 1 | ZG200-400 | Cast 20# |
| 15 | Nameplate | 1 | 0Cr18Ni9 | SUS304 |
| 16 | Climbing pole | 1 | 0Cr18Ni9 | SUS304 |
| 17 | Gas-freeing cover or V-valve cover | 1 | ZG200-400 | Cast 20# |
Technical Parameters:
| Type | Desinged Opening Pressure（Kpa) | Rated Working Pressure (Kpa) | Hydraulic Test Press (Mpa) | Velocity (m/s) | Rated Flow Rate(m3/h) | |||
| Pressure Valve | Vacuum Valve | Pressure Valve | Vacuum Valve | Pressure Valve | Vacuum Valve | |||
| DF50 | 14~20 | -3.5 | 21 | -7 | 0.345 | ≥30 | 300 | 300 |
| DF65 | 400 | 400 | ||||||
| DF80 | 600 | 500 | ||||||
| DF100 | 800 | 600 | ||||||
| DF125 | 1000 | 800 | ||||||
| DF150 | 2500 | 2200 | ||||||
| DF200 | 3000 | 3000 | ||||||
| DF250 | 3500 | 3000 | ||||||