Monday, October 9, 2017

Considerations When Applying Inline Spring-loaded Check Valves

spring loaded in-line check valve
Cutaway view of connector style spring loaded
in-line check valve.
Image courtesy Check-All Valve
1) Installation and Mounting

Inline, spring loaded check valves can be used in horizontal or vertical applications with proper spring selection. This is most evident in vertical flow down installations. The spring selected must be heavy enough to support the weight of the trim in addition to any column of liquid desired to be retained.

2) Elbow's, Tee's or other Flow Distorting Device's
Inline, spring loaded check valves are best suited for use with fully developed flow. Although there are many factors affecting the achievement of fully developed flow (such as media, pipe roughness, and velocity) usually 10 pipe diameters of straight pipe immediately upstream of the valve is sufficient. This is particularly important after flow distorting devices such as elbows, tees, centrifugal pumps, etc.

3) Valve Material Selection
There are many factors that influence the resistance of materials to corrosion, such as temperature, concentration, aeration, contaminants, and media interaction/reaction. Special attention must be paid to the process media and the atmosphere where inline check valves are applied. It is always recommended that an experienced application tech be consulted before installation.

4) Seat Material Selection
Several seat material options are available for inline, spring loaded check valves. An allowable leakage rate associated with the “metal-to-metal” as well as the PTFE o-ring seat, is 190 cc/min per inch of line size, when tested with air at 80 PSI. Resilient o-ring seats can provide a “bubble tight” shut-off (no visible leakage allowed at 80 PSI air).

5) Sizing and Spring Selection
It is very important to size check valves properly for optimum valve operation and service life. Sizing accuracy requires the valve be fully open, which occurs when the pressure drop across the valve reaches or exceeds three times the spring cracking pressure. Again, it is recommended that an experienced application tech be consulted for help with sizing.

6) Shock-Load Applications
Inline, spring loaded check valves are not designed for use in a shock-load environment, such as the discharge of a reciprocating air compressor. These types of applications produce excessive impact stresses which can adversely affect valve performance.

7) Fluid Quality
Inline, spring loaded check valves are best suited for clean liquids or gasses. Debris such as sand or fibers can prevent the valve from sealing properly or it can erode internal components or otherwise adversely affect valve travel. Any particles need to be filtered out before entering the valve.

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