The Metraloop pioneered by Metraflex and associated Dog Leg and V-Loops are the most dynamic way of allowing pipe movement available on the market. The Metraloop incorporates proven hose and braid technology into standard piping practices. One of the biggest advantages of using a Metraloop family product in lieu of traditional hard pipe loops or in line bellows expansion joints is the reduced anchor loads. You can see this in the side by side comparison below, using the same criteria, the Metraloop has an anchor load of 202 lbs. force versus 12,800 lbs. for a bellows or 780 lbs. for the much larger hard pipe loop. The reduced anchor load goes hand in hand with reduced guiding requirements, both are important features since designers often have a hard time restraining the loads associated with in line bellows expansion joints. The Metraloop also offers advantages over the traditional hard pipe loop by being much smaller and less expensive to construct.
The general Metraflex recommendation is that one guide be used on each side of the Metraloop. The actual recommendation is for a guide to be used on each side of the Metraloop if any of the hanger rods deflect 5° or more.
This is a general recommendation, not knowing anything about the application.
The function of guides for Metraloops are somewhat different than guides used for bellows expansion joints. When using Metraloops piping should be guided to restrain the piping since the Metraloop is a flexible element and could allow the pipe to move out of plane. For bellows expansion joints the guides are used to prevent exceeding the columnar strength of piping and potential pipe buckling due to the end loads developed by the bellows.
The reality is that the Metraloop itself does not need guides. And in straight pipe runs with anchors at both ends, guides will add little to no value and can often be omitted.
For the typical thermal (expansion or contraction) system the Metraloop can be placed anywhere between the anchors provided the return fitting is free to move, allowing each leg to flex equally.
Most installers choose to install Metraloops equidistant between anchors, as shown below.
When the pipe expands, the legs of the Metraloop absorb the movement as shown below.
However, if it is more convenient to install the Metraloop off center between the anchors, that will still work.
Notice that the Metraloop shown below absorbed the movement in both legs evenly. As long as the return fitting is free to move, the loop will be self-equalizing.
When the Metraloop is installed horizontally or vertically, the 180˚ return fitting needs to be supported in such a way that it is allowed to flex. The exceptions to this rule are self-supporting loop that do not require additional support of the return.
2.5” Diameter and smaller stock loops +-4” Movement and 2” Diameter and smaller stock loops +-8” movement are self-supporting. Additionally, all loops hanging down are self supporting
Stock Metraloops will have one support lug on the 180° return. Nested loops with spool pipes 24” or longer will have two support lugs installed 3” from the weld to the elbow.
For horizontal installations, support must be provided to prevent the loop from sagging for stock Metra loops 3” diameter and larger. The hanger rod must allow the 180˚ return fitting to move horizontally. A Spring hanger or swivel hanger is recommended.Horizontal is the recommended installation for STEAM applications
For horizontal installations, the return fitting can also be supported with a slide support for stock Metraloops 3” diameter and larger. The slide support must allow the 180˚ return fitting to move horizontally. Horizontal is the recommended installation for STEAM applications.
For horizontal pipe runs with the Metraloop hanging down, no additional support for the 180˚ return fitting is required.
For horizontal installations in vertical pipe runs, support must be provided to prevent the loop from sagging for stock Metraloops 3” diameter and larger. The hanger rod must allow the 180˚ to move horizontally.
For vertical installations in horizontal pipe runs, support must be provided to prevent the loop from sagging for stock Metraloops 3” diameter and larger.
The hanger rod or support must be spring loaded to allow the 180˚ to move up and down.
For large diameter Metraloops (12” and larger) additional support may be needed to prevent the weight of the wittings acting on the hose. Check with Metraflex Engineering.
To take advantage of the Metraloop family of products low anchor loads, Metraflex offers a easy to install bolt down anchor clamp, the PA Anchor. The PA Anchor can not be used with any in line bellows products.
- All the above information applies to V Loops and Dog Legs equally to Metraloops
- For steam applications make sure to check the steam rating for the loop and use double braid. For steam connections use either a raised face flange or weld ends.
- For potable water applications use UPC listed copper Metraloops
- For flammable gaseous and liquid fuel line applications use the CSA listed Metraloop
- For fire sprinkler applications use either the UL or FM Fireloop.
- For applications that require compliance with ANSI B31.3 consult Metraflex for additional requirements.
- For questions not covered here, please consult Metraflex