Abstract: A heat exchanger unit for use with spas or hot tubs. The unit is constructed to be installed in a side wall of a portable spa or hot tub. The unit has an exposed front plate or panel, and the unit is constructed so as to limit the temperature to which this panel can reach. The heater unit includes a finned tube construction and a blower with a double impeller. Flue gases enter into one end of the blower unit, and fresh air enters this end and also the opposite end so that the flue gases mix with fresh air. The discharge from the blower is through louvers in the front panel. The temperature of the front panel does not rise above a limiting value. The heat exchanger unit is automatically controlled and controls the temperature of the water in the spa or hot tub. A control is provided including a pitot tube positioned in the blower outlet whereby to shut down the system in the event of absence or failure of flow of gases which could allow the temperature to rise above the limiting value.

Abstract: Securement of flat heat exchange surfaces, particularly fins to tubular conduits of a heat exchanger. The heat exchange material is formed into upper and lower, or first and second pieces having longitudinal, partially circular recesses parallel to the length of a tube for engaging opposite sides of the tube. The radii of the recesses corresponds to the outer diameter of the tube. The recesses extend through less than 180.degree. so that the flat parts of the heat exchange surface are spaced leaving a gap prior to securement to the tubes. The two pieces are initially formed to interengage in such a way that they can be joined by lock seaming on opposite sides of the tube. Forces are applied to the interengaged pieces, forcing them together, stretching the heat exchange material at the recesses, thereby producing a tight interference fit between the heat exchange surfaces and the tube to provide minimum resistance to conduction of heat and at the same time securing the pieces together by lock seaming.

Abstract: Securement of flat heat exchange surfaces, particularly fins to tubular conduits of a heat exchanger. The heat exchange material has longitudinal, partially circular recesses parallel to the length of a tube for engaging opposite sides of the tube. The radii of the recesses corresponds to the outer diameter of the tube. The recesses extend through less than 180.degree. so that the flat parts of the heat exchange surface are spaced prior to securement to the tubes. Forces are applied normally to the surfaces, forcing them together, stretching the heat exchange material at the recesses, thereby producing a tight interference fit between the heat exchange surfaces and the tube to provide minimum resistance to conduction of heat. Securement may be by spot welding, riveting, or otherwise. The tube remains round and undeformed so the cross sectional heat exchange area remains the same.

Abstract: A servo valve control system exemplified by way of temperature controlled gas valves. Multiple slave pressure regulating valves are utilized supplying multiple burner manifolds. The first valve of the group of valves is modulated in response to temperature. The outlet pressure of each valve is utilized to bias and thereby modulate the next pressure regulating valve. The first valve, preferably is also controlled in response to an outdoor temperature sensor.

Abstract: An automatic flushing and cleaning system for membrane separation machines such as reverse osmosis machines having plural modules or membranes. Cleaning may be by way of reducing the pressure to allow the membrane to relax, by the injection of air or inert gas to provide turbulence, and/or by injection of flushing liquid which may include chemical cleaning additives. Pumps, automatic valving, and pressure controls are provided, along with a complete timer operated electrical sequencing system whereby desired purging, flushing and cleaning cycles are automatically undertaken at periodic intervals or in response to one or more preferred conditions.

Abstract: Porous, tubular core sections coated with a semipermeable membrane are joined at their ends by a simplified coupling member. Each coupling member or connector comprises a cylindrical flange member having circularly barbed or serrated nipples which fit tightly into the ends of bores of adjacent core sections. The ends of the cores abut against the circular part of the coupling member. Surrounding the joint thus formed is a flexible, elastomeric sealing sleeve. The nipples on the coupling member are axially slotted and have neck parts of a smaller diameter adjacent the body part of the coupling member providing annular openings between these neck parts and the bores of core members permitting continuous flow of permeate and cleaning solution without there being appendages, cavities, or pockets in which permeate or cleaning solution could be trapped.