Archive for year: 2019

PN, Class, K, bar are all units of pressure rating to express the nominal pressure rating for pipelines, valves, flanges, pipe fittings or fittings. The difference is that the pressure they represent corresponds to different reference temperatures. PN refers to the corresponding pressure at 120℃, while CLass refers to the corresponding pressure at 425.5℃. Therefore, the temperature should be taken into account in pressure conversion.

PN is mostly used in European standard systems such as DIN, EN, BS, ISO and Chinese standard system GB. Generally, the number behind “PN” is an integer number denoting pressure classes, approximately equivalent to normal temperature pressure Mpa. For valves with carbon steel bodies, PN refers to the maximum allowable working pressure when applied below 200℃; For cast iron body, it was maximum allowable working pressure when applied below 120℃; For stainless steel valve body, it was maximum allowable working pressure for service below 250℃. When operating temperature increases, meanwhile the valve body pressure decreases. Commonly used PN pressure range is (unit of Bar): PN2.5, PN6, PN10, PN16, PN25, PN40, PN63, PN100, PN160, PN250, PN320, PN400.

Class is the common valve pressure rating unit of the American system, such as Class150 or 150LB and 150#, which all belong to the American standard pressure rating, representing the pressure range of pipeline or valve. Class is the calculation result of the binding temperature and pressure of a certain metal according to ANSI B16.34 standard. The main reason pound classes do not correspond to nominal pressures is that their temperature benchmarks are different. The pressure of a gas is referred to as a “psi” or “Pounds per square inch”.

Japan mainly use the unit of K to indicate the pressure level. There is no strict correspondence between nominal pressure and pressure grade due to their different temperature reference. The approximate conversion between them is shown in the table below.

 

The conversion table between Class and Mpa

Class	150	300	400	600	800	900	1500	2000	2500
Mpa	2.0	5.0	6.8	11.0	13.0	15.0	26.0	33.7	42.0
Pressure rating	medium	medium	medium	high	high	high	high	high	high

 

The conversion table between Mpa and bar

0.05(0.5)	0.1(1.0)	0.25(2.5)	0.4(4.0)	0.6(6.0)	0.8(8.0)
1.0(10.0)	1.6(16.0)	2.0(20.0)	2.5(25.0)	4.0(40.0)	5.0 (50.0)
6.3(63.3)	10.0(100.0)	15.0(150.0)	16.0(160.0)	20.0(200.0)	25.0(250.0)
28.0(280.0)	32.0(320.0)	42.0 (420.0)	50.0(500.0)	63.0(630.0)	80.0(800.0)
100.0(1000.0)	125.0(1250.0)	160.0(1600.0)	200.0(2000.0)	250.0(2500.0)	335.0(3350.0)

 

The conversion table between lb and K

Lb	150	300	400	600	900	1500	2500
K	10	20	30	40	63	100	/
Mpa	2.0	5.0	6.8	10.0	15.0	25.0	42.0

 

The globe valve is designed with a stem that moves up and down to allow the medium flow one-way movement and make the sealing surface of the valve disc and seat tightly fit to prevent medium flow. It’s characterized saving elbow and operate conveniently and can be installed in the bent part of the pipeline system. There are various types of globe valve and designs, each with their own pros and cons. In this blog, we will introduce the classification of globe valves in details.

 

The flow direction of globe valve

1. Tee shape/Split body globe valve
   The design making inlet and outlet channels of the valve are 180° in the same direction and has the lowest coefficient of flow and highest pressure drop. Tee/Split type globe valve can be used in severe throttling services such as in bypass line around a control valve.
2. Y pattern globe valve
   Its disk and seat or the seat sealing an inlet/outlet passage present a certain angle, usually 45 or 90 degrees to the pipe axis. Its fluid hardly changes flow direction and has the least flow resistance in the globe valve types, suitable for coke and solid particles pipeline.

3. Angle pattern globe valves

Its flow inlet and outlet are not in the same direction with a 90° angle, which produces certain pressure drop. The angle globe valve is characterized by its convenience and without the use of an elbow and one extra weld.

 

Stem and disc of globe valves

1. Outside screw stem stop valve
   The stem thread is outside of the body without connection with the medium to avoid the corrosion, easy to lubricate and operate.
2. Inside screw stem stop valve
   The inner valve stem thread contact directly with the medium, easy to be corrosion and cannot be lubricated, usually used in the pipeline with the small nominal diameter and the medium working temperature is not high.
3. Plug disc globe valve

Plug valve is also known as the plunger globe valve. With a radial sealing structure design, by the polished plunger on the two elastic sealing ring through the body and bonnet connection bolt applied on the bonnet load around the elastic sealing ring to achieve the sealing of the valve.

4. Needle globe valve

Needle globe valve is a kind of small diameter instrument valve, which plays the role of opening and closing and flows control in instrument measuring pipeline system.

5. Bellows globe valve

Formed stainless steel bellows design offers reliable sealing performance, suitable for flammable, explosive, toxic and harmful media occasions, can effectively prevent leakage.

 

Applications of globe valves

1. PTFE-Lined globe valve
   PTFE Lining globe valve is the valve that molding(or inset) Polytetrafluoroethylene resin in the inner wall of the metal valve pressure piece (the same method applies to all kinds of pressure vessels and pipe accessories lining) or the outer surface of the valve inner piece to resist the strong corrosive medium of the valve. PTFE lined globe valve is applicable to Aqua regia, sulfuric acid, hydrochloric acid and various organic acids, strong acids, strong oxidants at various concentrations of -50 ~ 150℃, as well as strong alkali organic solvent and other corrosive gases and liquid medium in the pipeline.
2. Cryogenic globe valve
   Cryogenic globe valves usually refer to valves operating below -110℃. It is widely used in liquefied natural gas, petroleum and other low-temperature industries. At present, the globe valve with an applicable temperature of -196℃ can be manufactured, which uses liquid nitrogen for low-temperature pretreatment to completely avoid sealing deformation and leakage.

PERFECT manufacture and supply globe valves according to ANSI and API standards, the valve disc and seat sealing surface are made of stellite cobalt carbide surfacing that offering various advantages like reliable sealing, high hardness, wear resistance, high-temperature resistance, corrosion resistance, abrasion resistance and long service life. We design each valve according to the flow parameters presented. Contact our sales representative for details.

Valve actuators refer to devices that provide linear or rotary movement of the valve, which using liquid, gas, electricity or other energy sources and converted it by motors, cylinders or other devices.

Pneumatic actuator uses air pressure to realize the valve drive open and close or regulation with one piece implementation and regulation mechanism, can be divided into the membrane, piston and rack and pinion pneumatic actuator. The pneumatic valve structure is simple, easy to operate and check, can also easily achieve the positive reaction of the exchange, more economical than electric and hydraulic. It is widely used in power plant, chemical industry, oil refining and other production processes with high safety requirements.

Electric actuator has a large torque, simple structure and easy to maintenance, can be used to control air, water, steam and corrosive media like mud, oil, liquid metal, radioactive media and other types of fluid flow. It also has good stability, constant thrust and good anti-deviation ability. Its control accuracy is higher than the pneumatic actuator and can well overcome the imbalance of medium, mainly used in power plants or nuclear power plants.

When selecting a valve actuator, it is necessary to know the type of valve, torque size and other issues. Generally in the term of the structure, reliability, cost, output torque and other terms to consider. Once the actuator type and the drive torque required for the valve are determined, the actuator manufacturer’s data sheet or software can be used for selection. Sometimes the speed and frequency of valve operation should be considered. Here we collect some tips or suggestion for the actuators  choices:

Cost
The pneumatic actuator must be used together with valve positioner and air source, and its cost is almost the same as the electric valve. In water and sewage treatment, most valve actuators are operated in on/off mode or manually. The monitoring functions of electric actuators, such as overtemperature monitoring, torque monitoring, conversion frequency and maintenance cycle, must be designed in the control and test system, which leads to a large number of line input and output. In addition to terminal position sensing and air source handling, pneumatic actuators do not require any monitoring and control functions.

Security
Electric valves are an electric power source, circuit board or motor failure prone to spark, generally used in the environmental requirements are not high occasions. Pneumatic actuators can be used for potentially explosive occasions, and it is worth noting that the valve or valve island should be installed outside the explosion area, the pneumatic actuators used in the explosion area should be driven by trachea.

The service life
The electric actuators are suitable for intermittent operation, but not for continuous closed-loop operation. Pneumatic actuators have excellent overload resistance and are maintenance-free, requiring no oil change or other lubrication, with a standard service life of up to one million switching cycles, which is longer than other valve actuators. In addition, pneumatic components with high vibration resistance, corrosion resistant, strong and durable, even not damage at a high temperature. Electric actuators consist of a large number of components and are relatively easy to damage.

Response speed
Electric actuators run slowly than pneumatic and hydraulic actuators, it takes a long time from the regulator output signal to response and movement to the corresponding position. There is a great loss of energy when the supplied energy is converted into motion. Firstly, the electric motor converts most of the energy into heat, and then it uses gears with a complex structure. Frequent regulation will easily cause the motor to overheat and generate thermal protection.

Essentially, the main difference between electric and pneumatic valves is the use of actuators and has nothing to do with the valve itself. Choose which actuator to use that depends on the operating conditions, such as a chemical application or explosion protection or wet environment where need pneumatic valve and an electric valve is ideal for large diameter piping system.