37 Installation, maintenance, and repair of industrial equipment and heat transfer products, namely, heat exchangers, flow meters, pressure gauges, temperature gauges, pressure transmitters, temperature transmitters, control valves, instrument valves, tank valves, gate valves, plug valves, ball valves, check valves, butterfly valves, safety relief valves, manifold valves, pneumatic liquid level controllers, engine exhaust silencers, high velocity discharge silencers, air-intake silencers, pumps, filters, separators, and coalescers, tubes, and tube fittings