API 526 Spring Loaded Flanged Pressure Relief Safety Valve
Design Features:
1. Size Available 2"-12"
2. The 7110 series outlet port has the same size with inlet
3. The 8110 series outlet port is one size larger than inlet in order to optimize flow capacity
4. Vent to atmosphere
5. The weather hood and cover can be easily moved for inspection and maintenance
6. Protective screens are provided at pressure and vacuum port to prevent entrance of other matter
7. The flame arrestor, inlet pipe, steam jacket, blowing hole, lining or humidity absorber are options to clients.
8. Designed and tested according to API2000.
9. The flanges are accordance with ANSI B16.5, EN1092, JIS.
10. Available material: Aluminium, carbon steel, stainless steel, special materials.
Pressure Vacuum Relief Valve
The pressure / vacuum vlave is a protection device mounted on a nozzle opening on the top of a fixed roof atmospheric storage tank. Its primary purpose is to protect the tank against rupturing or imploding. Without an opening or a controlled opening. a fixed roof atmospheric tank would rupture under increasing pressure caused by pumping liquid into the tank or as a result of vapor pressure changes caused by severe thermal changes.
Imploding, or the collapsing of a tank, occures during the pumping out procedure or thermal changes. As the liquid level lowers, the vapor space pressure is reduced to below atmospheric pressure. this vacuum condition must be alleviated through a controlled opening on the tank. In short, the tank needs to breathe in order to eliminate the posiibility of rupturing or imploding. Because of its primary function, a Pressure/ Vacuum vlave is commonly referred to as a " breather valve "
• Pressure Relief : As the pressure in the storage tank increases, the vacuum pallet is held shut. When the set pressure is reached, the pressure pallet lifts and relieves to atmosphere. (or to a header if it a pipe away valve)
• 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 from the atmosphere.
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.
Pressure/Vacuum Valve Operation
How Pressure/Vacuum relief valves operate
How does a pressure/vacuum valve operate? Most atmospheric tanks require a venting device that will allow large volumes of vapor to escape under relatively low pressures.
Usually the allowable set pressure is in inches of water column pressure, both for positive and vacuum conditions. This is because most large storage tanks have a relatively low maximum allowable working pressure. These tanks are generally large volume welded vessels that are built to API650 standard.
In order to accommodate large volumes at low set pressures, these valves have ports that are greater in area than the inlet or nozzle connection.
The low setting required necessitates weight loading the valve as opposed to spring lading. Because of the above, a pressure/vacuum valve requires approximately 100% over set pressure in order to reach full opening of the valve. However, when deciding on a set pressure the weight-loaded valve operation MAWP should be at least twice the required set pressure to obtain optimum flow. If the MAWP is less than100% above the required set, valve could be larger in size than normally required. The possibility of valve chatter and accelerated seat and diaphragm wear will exist if less than 20% over pressure is allowed.
Simply stated, a pressure/vacuum valve is not exactly like a high pressure safety relief valve and should not be sized at 10% or 20% over pressure. When sizing a pressure/vacuum valve, consult the manufacturer flow curves and allow sufficient overset pressure.
PRESSURE/VACUUM VALVES SAVE MONEY
Actually, any properly sized opening in the tank's upper structure protects the tank from damage, but utilizing a pressure and vacuum valve also serves to accomplish other advantages. Two of the more important are: economic savings and fire hazard protection. In 1952, American petroleum Institute developed a formula to determine tank evaporative losses. The API equation was formulated after the results of a total of 256 individual tests were compiled.
Of the 256 tanks tested (½ with open vents and ½ with pressure/vacuum valves), only 178 were considered valid. The remainder was eliminated because of inadequate data, obviously incorrect test methods, poor tank conditions, or leaky fittings. The API has a formula for calculating tank breathing loss. The principle factors are turnovers per year, true vapor pressure of the product, diameter of the tank in feet, the average daily ambient temperature change, and the paint factor.
The test was conducted on tanks containing gas-line with pressure and vacuum valves set at oz. pressure and ½ oz. vacuum. API2521 states that ½oz. is the usual setting.
REDUCED CORROSION
An additional reason for using pressure/vacuum valves, they help reduce overall corrosion in the plant. Plant corrosion is reduced due to less product escaping from the tank and therefore less corrosion is produced by escaping vapors. This means overall plant maintenance is reduced thereby saving labor and dollars.
RECOMMENDED AND REQUIRED
Pressure/vacuum valves are recommended by API 2000 for use atmospheric storage tank in which oil with a flash point below 100ºF is stored. OSHA states that tanks storing Class 1 liquids shall be equipped with venting devices which shall be normally closed except under pressure or vacuum condition. Generally speaking, the majority of the regulatory bodies dealing with tank safety, API, OSHA, NFPA, Insurance Companies etc. require installation of these devices on flammable liquid storage tanks.
Factory Corner
Test & Inspection
FAQ
Q.
Are you a trading company or a manufacturer?
A: We are a manufacturer as you can see our workshop as above.
Q.
What is your payment term?
A:Normally T/T 30% in advance, balance to be paid before delivery.
Q:
What is your main market?
A:North America,Greenland,South America,Africa,Southeast Assia, Former Soviet Republics ,East Assia,and Europe.
Q:
Can I place sample order to your factory?
A: Yes, Samples can be provided.
Q:
What kind of trade terms can you do?
A:EX-WORKS,FOB,CFR,CIF,etc.
Q:
How long is your delivery time?
A: Generally it is 5-7 days if the goods are in stock. Or it is 15-20 days if the goods are not in stock, it is accordijng to quantity.
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