Valve World Magazine August 2022 - Sample | Page 39

Figure . 2 Figure . 3 Figure . 4 π

Technical

The use of auxiliary valves ( Axy ) on DIB-2 : Part 1

Auxiliary valves
( Axy ) are needed to conduct in-service maintenance and repair on pressurized gate or ball valves in a safe manner .
Axy valves should be used in combination with service valve for throttling . This is part 1 of the article , the second part will be published in Valve
World August .
By Ingolf Holmslet

Axy valve™ is an auxiliary valve installed in the cavity of a gate or a ball valve , with the purpose of controlling , testing , setting barrier or performing maintenance on the main valve . iSmart™ ( in-service maintenance and repair technology ) is service , maintenance , on gate or ball valves performed in line under pressure . To perform iSmart , you need Axy valves installed in the cavity vent or cavity drain on the main valve . All parallel gate , large wedge gate and ball valves will be equipped with a blind or a bleed plug in the cavity . One can ask , what is the purpose of a blind or a bleed plug ? And the answer is , to plug off the hole or to bleed out of the cavity when the valve is without pressure . Some claim that a bleed plug , or a grease fitting can be used to drain the valve cavity . In most cases this is not correct . It is not only not correct , but it could also be dangerous . In the worst case , people could get seriously hurt .

Not safe
Let me explain . You would never open a blind plug with pressure on the inside of the plug . On most bleed plugs the bleed hole is small and if opening with high pressure gas on the inside , you risk hydrate plugging the bleed hole . If you try to bleed through the bottom bleed plug , you may have a clogged bleed plug , giving you the wrong
Figure . 1
idea that there is no pressure on the inside . If you open a bleed plug under pressure , you may also risk that you are unable to close off the bleed plug . Bleed plugs are available in several configurations . Figure 1 shows three different types with two different outlets . Some bleed plugs have a small outlet ( 2-4 mm ). Others can go up to 8-10 mm but these are not safe for use under pressure . I would never recommend using a bleed plug in pressurized conditions as you cannot trust them .
Two valves
Therefore , it is important to install Axy valves in the cavity . An Axy valve consists of : * an inlet connection , this can be RTJ flange ( as in Figure 2 ), compact flange or NPT threads as per the users preference .
Difference between modular and Axy valves ?
The question arises , what is the difference between a modular valve and the Axy system ? Consider the wedge gate modular valve shown in Figure 3 . Whilst there is nothing inherently wrong with this valve , it is important to be aware that the construction can result in several disadvantages . 1 ) The modular valve consists of two block valves and a bleed valve in one body . That makes the valve relatively large . Due to this the valve needs a lot of space for installation . 2 ) It becomes quite heavy and if the connection to the main valve is NPT threads it is a lot of weight on those threads . If that valve should be installed into threads , it would need extra supporting .
3 ) When using the modular valve , the inner valve will be opened first to protect it . When using valve number two as a throttling valve that valve will in all probability start to leak at a given moment . To repair the modular valve , you must shut down to replace it or replace the whole modular valve .

Figure . 2 Figure . 3 Figure . 4 π

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