Applies for all check valves.
In some installations check valves may require special attention to function satisfactorily.

1. Small pulsating gas flows
NAF-Check opens quickly for a low differential pressure. It also closes very quickly when the differential pressure lessens. If the flow pulsates and is so low that the valve is not fully open, the valve disc may flutter resulting in unnecessary wear. Piston compressors and steam digesters for direct infusion of steam to heat water are examples of components that may give difficult pulsations.
Remedy: Is the flow large enough to eliminate the risk of flutter with a valve of full pipe size? If not, choose a smaller valve so that it will be fully open in all normal operation cases.

2. Low pressure gases - vacuum
The opening dynamic force is affected by density. A low pressure gas requires a larger flow that a high pressure gas to fully open the valve.
Remedy: Make certain that the available differential pressure, flow velocity and density are adequate.

3. Location on suction side of centrifugal pumps
A centrifugal pump has certain pressure requirements on the suction side (NPSH) to be able to start pumping and avoid cavitation. The pump manufacturers recommend an open pipe on the suction side.
Remedy: Place the check valve behind the pump. Even though NAF-Check opens easily, it will reduce the suction pressure if placed on the suction side.

4. Pumps in parallel
Attempts to start the second of two pumps in parallel having rising QH-curve, while the first pump is still working, will result in the check valve not opening. The pressure behind the valve will be higher than in front of it.
Remedy: Make certain that the pump characteristics fall the entire flow range. Otherwise special measures such as throttling and shunting will be necessary.

5. Downward flow
NAF-Check - as well as swing check valves and other tilting disc swing check valves - is intended to be mounted in horizontal lines or vertical lines with upward flow. It can also be installed in oblique lines with upward flow but installation in lines with downward flow should be avoided.

Introduction
Installation & Maintenance
PN 25-40-100 Class
ANSI 150-300
Certification
Sizing & Pressure Drop