How to handle thermal contraction

Standard bellows expansion joints are designed to primarily handle compression resulting from pipe expansion. In the case of a pipe contracting due to a chilled system media, the expansion joint should be pre compressed at the factory to allow the extension of the joint when the pipe contracts.

Do I need control rods on a hose and braid pump connector?

No, The braid acts as the control rods. The rods would be redundant and might limit the vibration isolation ability of the hose and braid pump connector.

Why is my check valve chattering?

The most common reason a check valve chatters is turbulence.  Very often the turbulence is caused because the check valve is installed too close to the discharge of a pump or is just downstream of an elbow or some other turbulence causing device. Valve manufacturers, including Metraflex recommend 5-10 straight diameters of pipe directly upstream of the check valves. This allows any turbulence in the system to settle out prior to reaching the check valve. Turbulent flow will cause the disc to be loaded in a random way causing the disc to flutter and bounce.

There are two possible solutions if your check valve is chattering:

1. Move the check valve further downstream from any turbulence causing equipment.

2. Install a Vane Flex, a flex connector with built in straightening vanes, upstream of the check valve.

What if my pressure requirements exceed the rating the flexible connector’s submittal?

For higher pressure applications, we can add a second layer of braid (double braided) to the flexible connector. This second layer of braid adds extra tensile strength to the connector, allowing it to have a higher-pressure rating than the standard option.  There are also higher-pressure hoses available as well.

For high pressure applications, please contact The Metraflex Company.

When do I need to add a liner to a hose or expansion joint?

There are three reasons you would want to specify including a liner for a hopes or expansion joint.

1. For internally pressurized bellows the requirement for needing a liner is spelled out in EJMA (Expansion Joint Manufacturers Association) per the table below.

For a hose the requirement for needing a liner is more straight forward.  Any liquid application of 25 feet per second or gas application over 75 feet per second should have a liner.

2. Any applications that are erosive or have particulate matter that may damage the hose.

3. For plumbing applications where the pipe may need to be rodded to clear an obstruction. An example of this would be the DWV Metraloop.

Please note: Externally pressurized expansion joints by design have a built-in liner. Examples of externally pressurized expansion joints include Metragator, HP, and HPFF.

What kind of liner should I use?

This will depend on the type of product.

For internally pressurized joints, a solid liner is used that will not interfere with the bellows as shown below.  This type of liner can either be permanently welded in place or slipped into place.

Note.  Liners for internally pressurized bellows are flow dependent.

For hose products an interlock hose is used.  This will match the bend radius of the corrugated hose.