THE AVK Group
T he w e d g e i s t h e h e a r t
Don’t compromise with the quality!
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What if ...
At birth, you were able to choose your own heart.
Would you choose a cheap heart which broke down - sending you in and out of hospitals, or would you choose a quality heart that remained healthy and strong throughout your long life?
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Yo u h av e a cho is e b e t w e e n g o o d o r b ad q uality!
Just like you - a valve has a long lifespan. Thoughout it’s youth, all valves do well - but as times goes, wear and tear take their toil, and the differences between good or bad GOOD QUALITY
quality becomes apparant. The healthy quality valve will continue performing effortlessly, whilst the cheap valve will require more and more maintanance - at a very high cost! Get to know the differences between the healthy strong valves and those that are not - and let us tell you why your choise should be an AVK valve. Lorem ipsum dolor sit amet, consectetur adipscing elit, sed diam nonnumy eiusmod tempor incidunt ut labore et dolore magna aliquam erat volupat. Ut enim ad minim veniam, quis nostrud exercitation ulamcorper suscipit lab oris nisi ut aliquipex ea commodo consequat. Duis autem vel eum irure dolor in .
BAD QUALITY
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INDEX
Resilient seated gate valves page
06 - 07
Wedge design page
08 - 09
Fixed wedge nut page
10 - 11
Wedge guides page
12 - 13
Rubber bonding page
14 - 15
Compression set page
16 - 17
Rubber compound page
18 - 19
Biofilm on rubber surfaces page
20-21
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magna aliquam erat volupat. Ut enim ad minim veniam, quis nostrud exercitation ulamcorper suscipit lab oris nisi ut aliquipex ea commodo consequat. Duis autem vel eum irure dolor in . Lorem ipsum dolor sit amet, consectetur adipscing elit, sed diam nonnumy eiusmod tempor incidunt ut labore et dolore magna aliquam erat volupat. Ut enim ad minim veniam, quis nostrud exercitation ulamcorper suscipit lab oris nisi ut aliquipex ea commodo consequat. Duis autem vel eum irure dolor in
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B e s t c h o i s e f or an up d ated netwo rk: R e s i l i e n t seated g ate v alv es
The resilient seated gate valve has a plain valve bottom allowing free passage for sand and pebbles in the valve. If impurities pass as the valve closes, the rubber surface will close around the impurities while the valve is closed. Before the resilient seated gate valve was introduced to the market, gate valves with a metal seated wedge were used. The conical wedge design and angular sealing devices of a metal seated wedge require a depression in the valve bottom to ensure a tight closure. Herewith, sand and pebbles are embedded in the bore. The pipe system will never be completely free from impurities regardless how thorough the pipe is flushed upon installation or repair. For any metal wedge this will in time lead to inability to close drop tight. Tests prove that the rubber surface of a DN 250 wedge absorbs impurities up to Ă˜8.7 mm. A correct rubber compound is soft enough to absorb impurities, yet strong enough to wash the impurities through when the valve is reopened. Hereafter the rubber surface regains its original shape securing a drop-tight sealing.
Metal seated competitor valve – notice how sand and pebbles have settled in the sump.
A metal wedge does not close tight when sand and pebbles are embedded in the bore.
With a resilient seated gate valve all impurities are absorbed in the rubber while the valve is closed. When the valve reopens, the impurities pass and the rubber regains its original shape.
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• Low torque required for easy valve operation – either manually or by motorized actuator. • Positioned in the valve body by means of wedge guides for a safe shut-off function during frequent use at different water pressures. • Large safety margin against overload of min. 5 times the torque required to close the valve. • Ductile iron wedge body with fixed wedge nut of high strength alloy. • Total corrosion free wedge - the special vulcanization process developed by AVK GUMMI A/S secures total rubber covering of the metallic wedge core. • Resistant to differential pressures from -0.8 bar to 25 bar. • Approved for drinking water • In case of pebbles being trapped under the wedge, the rubber will still ensure full tightness. When the valve reopens, impurities pass and the rubber regains its original shape.
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T h e w e d g e d e s i gn makes q uality p o s s ib le
The wedge is designed and developed by the AVK Technology Centre and is thoroughly tested. It is based on AVK’s 40 years of experience with gate valves for water mains and is carried out according to ISO, EN, BS, AS, DIN, NF, AWWA, SABS and JIS standards. The rubber-bonded wedge is maintenance free and requires no adjustments. However, the design imposes extreme demands on the rubber quality and on the method used to bond the rubber to the metal core. Guides in the wedge and on the valve body ensure a uniform closure irrespective of the pressure, and a safe operation is secured as the guides also prevent overload of the stem. The fixed, integral wedge nut reduces the number of moveable valve parts and the consequent risk of malfunction. The wedge nut is made of desincification resistant brass which has lubricating abilities providing an optimum compatibility with the stainless steel stem.
These 2 pictures show failed wedges from other brands due to inferior rubber quality and/or rough layer thickness.
When the core is vulcanized with rubber it must be supported in connection with the inside vulcanization – here the support points have not been covered with rubber and corrosion will start as soon as the valve is in contact with water.
The wedge guide has an uneven rubber thickness which has resulted in an irregular load during operation. The rubber is destroyed and the core has been exposed which has resulted in corrosion.
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The rubber material is developed by AVK GUMMI A/S, one of the world’s most modern and leading manufacturers of rubber components. The design imposes high demands on rubber quality and on the method used to bond the rubber to the wedge body. The rubber is developed with particular focus on high tensile strength, flexibility and an excellent compression set (the ability to regain the original shape). Also, it is of decisive importance for the tightness and durability that the rubber is resistant to water treatment chemicals - e.g. ozone and chlorine. The ductile iron core is fully vulcanized with EPDM rubber both inside and outside. A minimum of 1.5 mm rubber is applied on all pressure bearing surfaces and minimum 4 mm on all sealing surfaces regardless the design. During the process, the metal wedge core remains untouched by man which may otherwise impede the bonding process between the metal core and the rubber. The excellent vulcanization prevents creeping and corrosion underneath the rubber.
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A f i x ed wed g e nut c o n t r a a lo o s e wed g e nut
The advantanges of a fixed wedge nut The fixed wedge nut reduces the number of moveable parts. The wedge nut is made of desincification resistant brass which has lubricating abilities. It provides optimum compatibility with the stainless steel stem. A wedge design with fixed wedge nut requires accurate and efficient wedge guides thus making sure that the stem does not bend at extreme flow velocity and that the wedge has an equal operating torque during the entire process from open to closed position. A plastic wedge shoe has been vulcanized into the rubber layer on the wedge guides for optimum protection of the rubber at repeatedly open/close operations. The interface between the wedge nut of desincification resistant brass and the ductile iron wedge core is covered with rubber to prevent galvanic corrosion between the two materials.
The disadvantanges of a loose wedge nut One of the most noticeable disadvantages of a loose wedge nut is that it is difficult to vulcanize inside the bayonet socket in the wedge. At best, a thin rubber layer is vulcanized only to be worn through. The loose wedge is influenced by the flow, and the vibration of the wedge will lead to abrasion on the wedge. The rubber layer on the bayonet will soon be worn through and corrosion will occur. The operating torque will be increased dramatically during high flow velocity as a wedge with loose wedge nut has a tendency to “edge� the valve body causing an increased friction between the rubber and the inside epoxy coating.
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We d g e G uid es
The AVK wedge has accurate wedge guides complying with very low tolerances. This requires an accurate and thorough vulcanization of the rubber. AVK uses rubber compounds durable enough to resist repeatedly open/ close operations. Furthermore, the friction against the valve body’s internal epoxy coating is very low with this rubber quality, whereby a very low free running torque and closing torques are achieved. The AVK wedge also features a vulcanized wedge shoe for protection of the rubber during open/close operations and to reduce the operating torque even further. The wedge shoe is an integral part of the wedge guides, and the unit ensures easy operation and long life.
The consequences of inadequate vulcanization The pictures show competitor wedges with loose wedge shoes. The vulcanization is particularly inadequate and there is hardly any rubber underneath the wedge shoe. When the loose wedge shoe is removed, it is obvious that the drinking water has been in contact with the wedge core, as corrosion has occurred.
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R u b b e r b o n d i n g - the key to a lo ng er lif e
The quality of the bonding between the rubber and the wedge core is of vital importance. The unique technique used by AVK includes a double bonding system to ensure optimum adhesion. The wedge core is immersed in two different baths - the first to prepare the ductile iron core and the second for vulcanizing the rubber to the core. Bonding has to be perfect, meaning that when peeling of rubber from the core, the core has to be covered with rubber. As no international standard is available AVK has developed its own harsh test method, providing credible results. Test is done both during production and after immersion in 90째 C water for 3 weeks. To ensure that the bonding between the materials meets the highest quality demands, AVK only uses unique AVK rubber compounds. The rubber is vulcanized to the metal wedge core with a process that fully bonds the two materials. If a sharp object penetrates the rubber, the core will not be exposed, thus preventing creeping corrosion underneath the rubber. The wedge has a large straight bore, and with no cavities in the core, stagnant water and impurities will not settle and cause pollution.
A competitior wedge is totally destroyed due to lack of bonding and incorrect vulcanization.
Rubber is peeled off the metal core due to insufficient bonding. As a result, rubber is peeled off during A bonding test showing poor adhesion. This could be induced by wrong choice of bonding system, wrong processing or contamination
normal operation.
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Bonding – 50 years' service life • 100 % rubber layer with min. 1.5 mm rubber. • No corrosion. • Wedge shoes 100% integrated in the rubber layer. • Minimum risk of bacterial growth. • Large smooth spindle hole. • Sufficient water replacement. • Fixed wedge nut. • Reduced wear.
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C o mp res s io n s et
The high quality rubber used in the wedge has an excellent compression set also called memory (the ability to recover the original shape after being compressed). Even after many years of operation, tiny pebbles, sand and other impurities will not affect the rubber surface or the tightness of the valve. We use unique AVK rubber compounds to ensure that the wedge can compensate the impurities in closed position and is able to regain its original shape when reopened.
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5 EN 681-1
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EUW-70
NGW-70
23ºC, 72 hours, 25%
EN 681-1
EUW-70
NGW-70
70ºC, 72 hours, 25%
The picture shows a competitor’s wedge which has been damaged because of its failure to resist the closing torque. It can no longer close tight and the drinking water now has free access to the wedge core with corrosion attack in consequence.
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Compression set (permanent deformation) The rubber is deformed by 25 % of its original thickness at a constant temperature for a specific time. The pressure on the rubber is relieved and the layer thickness is measured after half an hour. The smaller the deformation the better the memory effect.
Compression set (S) =
d0 - d1 d0 - d2
d0 = original thickness of the test specimen d1 = thickness of test specimen after test d2 = thickness of test specimen in compressed condition
EN 681-1 A common European standard stating the minimum requirements for the physical properties.
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R u b b er co mp o und
Chlorine and other chemicals are commonly used to clean new pipelines or disinfect old ones. Ozone and chlorine may also be added in low concentrations to make the water drinkable. AVK has developed an EPDM rubber resistant to such water treatment chemicals. The rubber, which is a complex formulation of many ingredients is developed and tested by AVK's own R&D scientists. For third party verification and approvals we work only with recognized test institutes. AVK has the most advanced state of the art mixing facility, offering high performance materials, with an equally high accurancy. Tests are continuously carried out to ensure that the correct rubber compound is applied for the right area of use, and that rubber used in drinking water does not give off taste, smell or colour. The rubber compounds are also ozone tested as exposure to ozone tends to have a negative effect on e.g. NBR.
A competitor NBR wedge with ozone cracks. After one month, distinct cracks occur in the rubber. If these cracks occur in the sealing surface it may result in creeping corrosion in the wedge core.
The following factors are of decisive importance for the functions
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of a rubber sealing: • Minimum permanent deformation
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140 128
• Resistance to water treatment chemicals - e.g. ozone and chlorine • Taste, smell and colour neutral Ozone resistance:
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120
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100
rubber materials, if such materials are not adequately formulated to
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Ozonation is commonly used to reduce smell and taste or to reduce bacterial activity. The chemical reaction will also cause degradation of
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80
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60
4
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encounter highly reactive chemicals such as ozone. AVK compound EUW-70 is superior to any other material, including many other EPDM materials. The unique structure can withstand even extremely high concentration of ozone. After 200 hours of exposure in 200 pphm EUW-70 does not change any properties, while both SAK-70 (AVK’s SBR grade) and NGW-70 (AVK’s NBR grade) are suffering”. With EUW-70 half a century of effortless operation is a reality.
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20 EN 681-1
0
EUW-70
NGW-70
Tensile strength in MPa
EN 681-1
0
EUW-70
NGW-70
Index wear resistance
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100
As chlorination of drinking water is common in most places it is important that the rubber is unaffected by long time exposure. AVK has developed a series of EPDM compounds - here illustrated
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by EUW-70 which is literately unaffected by even at extreme concentration of sodiumhypochlorite (NaOCl) - a commonly used source for chlorination.
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In the past SBR was often used for wedges, as this material is tough and cost efficient. However it is inferior to EUW-70 not least
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due to the poor resistance towards chlorination. AVK compound SAK-70 is a good but typical representative for SBR. NBR is often requested as it can be used for both water and gas applications,
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provided the compound has been approved accordingly. However EN 681-1
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EUW-70
Tensile strength
NGW-70
EN 681-1
EUW-70
Volume change
NGW-70
a compromise must be accepted, as also NBR - in this case our NGW-70 - will suffer too.
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B i o f i l m o n rub b er s urf aces AMOUNT
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Building of biofilm Organic substances as e.g.
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medicinal paraffinic oils and waxes migrate from the rubber compound. They act as nutrients for
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microorganisms which will then start forming biofilm. In the course of time, however, there
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will be fewer nutrients available, and the biofilm will decompose.
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2
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Competitor EPDM wedge after 6 months of operation - an example of microbiological growth on an improperly compound.
formulated
rubber
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MONTHS
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AVK wedge without Biofilm
Standards and approvals AVK is known as a manufacturer of high quality products supplying a wide range of products for the water supply throughout the world. AVK produces according to all common national and international standards such as ISO, CEN, DIN, NF, BS, GB, AWWA, JWWA, SABS, AS and GOST. All rubber compounds used in our products are manufactured by AVK GUMMI A/S which quality management systems is certified in accordance with EN ISO 9001 and ISO/TS 16949. These systems include 100 % control of each rubber compound, full traceability with the help of a charge number system, SPC control, FMEA and a zero defect production. The rubber is manufactured for the segments drinking water, food, health care and gas. A list for each segment is formulated to secure that only the correct additives are used in the process. In the area of drinking water applications, all rubber compounds are approved according to below standards as appear on the list to the left.
APPROVALS WATER: Approval
Country
KTW D1/D2
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DE
W 270
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DE
WRAS BS 6920
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UK
ACS XP P 41-250
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FR
ANSI NSF-61
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USA
AS/NZS 4020
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AUS
SS 375
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SN
JIS K6353
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JP
KIWA
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NL
Norm B 5014
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AU
NBN S29003
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BE
Hydrocheck
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BE
CSN 75 7111
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CZ
CSN 10774
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CH
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D o n ’t co mp ro mis e, c h o o s e f o r the f uture!
When you choose a valve from AVK, you get much more than meets the eye. You get 60 years of dedication and experience, you get research and developement on the highest level, you get products made from the best raw materials and a welldocumented production process. You also get a long range of international certifications, and a guarantee that our products live up to our promises! With an AVK valve, you give heart to a long, healthy life for your network with minimum maintenance and longterm savings.
Don't compromise with anything as important as the heart.
FIRE FIGHTING
GAS
S E WA G E WAT E R
C L E A N WAT E R
Choose quality and long life - choose AVK
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