Most European national standards bodies are members of this Committee and therefore they are bound to comply with the standards and implement them as national standards. So if a company¡¯s products comply with the standards outlined by CEN the products also comply with most national standards.
But what do these standards actually specify? In the following we will cover one of the major standards in our line of business - the EN 1074 standard - that outlines requirements and test conditions when designing valves for water supply.
EN 1074 incorporates provisions from other publications and as such also comprises standards as EN 558-1, EN 681-1 and EN 12982.
EN 1074 consists of six parts. Part 1 covers general requirements and test procedures whereas parts 2-6 are more detailed and covers certain types of valves.
part 2 - isolating valves
part 3 - check valves
part 4 - air valves
part 5 - control valves and
part 6 ¨C hydrants
The right material makes the difference
Materials, that are in contact with water intended for human consumption, must comply to the requirements in the National Regulations in the country of use, and must not affect the water in any way. This means that the chemistry and physical appearance of the water must not change after having been in contact with a valve ¨C you must not be able to see, smell, feel or taste any difference in the water. Also, all internal as well as external materials have to be resistant to corrosion or protected by appropriate means.
At AVK we have taken our precautions to be sure the water remains clean and fresh when using our products. We use drinking water approved EPDM rubber in our products for water. We use our own rubber to be certain of the ingredients and processes used. Read more about our rubber compounds here.
Furthermore, we coat our products in compliance with DIN 3476 part 1, EN 14901 and GSK making sure our products are highly resistant to corrosion. You can read more about our coating process here.
Designing in accordance with service life time and temperature specifications
For the water business, the standard states it is essential that the valves are designed for minimum 50 years¡¯ service life time and can withstand temperatures from 0⁰C to 40⁰C while in service and between -20⁰C and 70⁰C when stored. It is recommended that the resistance of the valve wedge is tested. The test has to be performed according to the stated temperature in service, while the pressure is maintained at least 10 minutes. If the material of the valve is of a so-called time-dependent material (e.g. plastic etc.) it is recommended that the valve must be pressure tested at a temperature corresponding to the surroundings as well as at an elevated temperature to demonstrate that the valve is designed for a 50 years¡¯ lifetime.
Other design considerations apply for i.e. industrial usages as well as for HVAC and building services where service life and temperature ranges typically can range up to 130⁰C for use in district heating.
In the design phase AVK makes sure that every single component in a valve meets the requirements and ask our suppliers to document this before choosing the material. The valves are thoroughly tested and approved by independent institutes such as DVGW if so required.
Tightness is essential
One of the most important requirements to a valve is tightness. You need to be aware of multiple parameters to be sure the valve is completely tight in relation to ingress of air, water or any foreign matter. First, the valve has to be tight while withstanding a certain amount of pressure from the water flowing inside. Valves for water must withstand a pressure equalizing 1.5 x their PN. When pressure tested the valves must not have any visual detectable leakage.
The valves also have to be controlled while in closed position and exposed to differential pressure. The valves therefore have to undergo a seat tightness test and an operational test.
Another focus point in the EN 1074 Standard is the tightness of valves when connected with pipes. It is essential, that the connection point between the valve and the pipe is tight even when bended and therefore the valves have to be designed according to bending measures specified by CEN.
At AVK the valves are bend tested in the development process. In the production every single valve is shell tested at 1.5 x PN with a clear specification of no leakage. Also the valves are seat tested with water at PN x 1.1 from both sides and with one end open.
Operating torques when testing for tightness and strength
The requirements for tightness while in closed position are the same as when open: 1.5 x PFA or PFA + 5. (PFA = Maximum continuous pipe line water pressure). To be able to pass both tests the closing and opening torque must not exceed the MOT.
If the valves are without an operating device and intended to be operated by a T-key the MOT is specifically defined for butterfly valves as 125Nm and for gate valves as 1 x DN Nm. Manually operated valves are to be closed with a torque equal to the maximum operating torque (MOT) and no leakage is to be detected.
The minimum operation strength in the closing and in the opening direction have to be equal to the minimum strength torque (mST), where the mST has to be equal to twice the maximum torque (MOT).
At AVK we test, not only with 1 x DN Nm, but we expect our products to be tight even when the torque is lower than the defined values. We test our valves down to 0,6 x DN depending on size.
Specification of MOT (Maximum Torque)
The MOT is dependent on the associated operating device. If the valve is delivered with a handwheel the MOT is defined as 0.5 x the maximum operating manual force (in Newtons) x the diameter of the handwheel (in metres). For valves delivered with a lever the MOT is defined as the maximum operating manual force (in Newtons) x the length of the lever (in metres).
Operating cycles while testing for endurance
Valves must be designed to last a period of minimum 50 years. Therefore they need to undergo an endurance test where they are subjected to the same tests several times in succession ¨C called operating cycles. The number of operating cycles a valve shall undergo to meet the endurance requirements depends on the type and size of valve. Each part of the EN 1074 standard specifies the requirements for each type of valves.
As the design of AVK valves is similar for handwheel-operated valves as for the ones with ISO flanges for electrical operation, all our valves up to DN1200 are designed for 2500 operations although only 250 cycles are required in the standard.
Required operating cycles
Manually operated isolating valves have to be designed for 250 cycles whereas electrically, hydraulically and pneumatically operated valves have to be designed for 2500 cycles. The pressure in all types of isolating valves, while filling with water, has to be at least what equals the valve¡¯s PN and maintained for at least five seconds.
Check valves have to be designed comprising 2500 opening/closing cycles.
Air valves have to be designed to be able to undergo 250 cycles of filling and draining while opening and closing the valve fully. The pressure of water while filling the valve has to be +/- 10% of their PN while maintained for at least two minutes.
Control valves have to be designed to have a differential pressure of +/- 10% of 1.5 x their PN while maintained for at least 15 seconds and repeated for 2500 cycles.
Hydrants have to be designed to undergo a differential pressure equal to their PN. The opening/closing cycle has to be of 1000 cycles.
Required test procedures
In the EN 1074 Standard, all test procedures are described in detail. It is essential that the tests are done on valves representative for the current production and that all the tests are recorded in test reports stating type, quantity, DN and PN as well as what equipment has been used and how the valves performed.
In the design phase AVK tests the valves according to the following requirements: EN 1074, EN 1171, official approval requirements like forex, DVGW, local market requirements and not least AVKs own requirements based on more than 40 years of experience with producing valves for drinking water supply systems worldwide.
In the production of valves according to EN 1074, we test every single valve before it is released for sale and the documents associated to the tests are all archived and can be located 20-25 years back.
Documents and marking
The quality of the valves also needs to be checked regularly and the quality system of the company needs to be controlled by a third party certification body.
AVK is certified in the product development and manufacture of valves according to the quality management system ISO 9001 ensuring consistent quality of the products, including processes to improve the system and to assure conformity, that comply with the legal requirements.
Finally, the EN 1074 standard states that products need to hold the correct marking; where DN, shell material, PN, ID and year of manufacturer, as well as the number of the relevant part of the EN standard 1074 have to be clearly stated.