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OSHA Safety Standards are US law and they contain requirements for "approval" (i.e., testing and certification) from testing laboratories approved by OSHA such as: a Nationally Recognized Testing Laboratory (NRTL) ETL ( Intertek), FM (FM Approvals), CSA (Canadian Standards Association) and UL (Underwriters Laboratories Inc.).
Natural refrigerants have no, or an insignificant, impact on the ozone layer and greenhouse effect. They are widely used in smaller applications, such as heating pumps, small chillers, and commercial systems.
The round shape of nodular graphite reduces the stress concentration and consequently, the material is much more ductile than grey iron. Nodular iron is normally used for pump parts with high strength requirements.
A non-return valve allows a medium to flow in only one direction. A non-return valve is fitted to ensure that a medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow.
The difference between inlet pressure and the lowest pressure level inside the pump is called NPSH (Net Positive Suction Head). NPSH is an expression of the pressure loss that takes place inside the first part of the pump housing.
NSF (National Sanitation Federation) is a non profit organization dedicated to public health safety and environmental protection. It does so by developing standards, providing education, and by providing third party conformity assessment services.