The liquid CO2 transfer pumps manufactured by Smith Precision Products of California are designed for moving large quantities of bulk carbon dioxide between two low pressure vessels, where the differential pressure does not exceed 4.8 bar, typically between a road tanker and a CO2 bulk storage tank. The complete range includes pumps with CO2 transfer capacities between 0.5 te/h and 35 te/h.
The Smith pumps use precision-cut, interlocking gears to propel the liquid carbon dioxide. The gears are lubricated by the liquid CO2 and hence run oil free. The shaft seal assembly which turns the drive gears is connected directly by means of a coupling to the electric motor and can be run at speeds of up to 1800 rev/min, although a slower running speed is recommended to prolong pump life.
The recommended shaft seal assembly contains a ‘Superseal’ sealing ring, which minimises seal wear. This ‘Superseal’ option on the pump is denoted by the addition of the letters ‘SS’ after the pump model number, e.g. Smith pump MC2SS.
Many of the Smith pump models are reversible, avoiding the need for cumbersome loading and discharge pipework arrangements. The inlet and outlet ports on the standard pumps have NPT female threads, although bodies with flange connections can also be supplied.
Pumps can be supplied with or without motor, baseframe, coupling and separate by-pass valve, if required.
Pump life can be considerably extended by the use of the high capacity (‘H’) range of pumps operated at a reduced speed.
Utilising a larger gear set the pump can achieve required transfer rates at lower speeds. In addition to a reduction in noise levels, operating the pump at half the recommended speed can extend the life of the pump by up to three times.
Standard Smith CO2 pumps are designed for intermittent duty and generally should not be operated for more than two hours at any one time.
Special pumps (NSSA Option) are available for use in installations requiring extended operating periods (for example in continuous re-circulation) or where higher than normal differential pressures are encountered. In these cases a larger pump running at a lower speed would be recommended to maximise pump life.
The NSSA option features gear sets made from aircraft quality steel (Nitralloy 135MOD) hardened with a special nitriding process to provide a very hard wearing surface. Special Tungsten Carbide idler gear shafts are fitted to provide rigidity under high load conditions.
Standard Smith CO2 pumps feature an ANSI standard female NPT thread connection. Installation must be made with a compatible sealant to produce a pressure tight joint.
An option is available to provide either screwed or butt weld companion connection which may improve access for maintenance.
The Smith by-pass valves can safely control and limit excessive differential pressure without cavitating the pump.
A by-pass valve properly installed provides a safe automatic product return through a separate circuit which allows generated heat and vaporisation to dissipate before the liquid CO2 passes once again to the pump inlet.
All Smith by-pass valves incorporate a unique flow plate to evenly dissipate flow when the valve opens. This eliminates chatter and minimises overpressure even at higher flow rates.
The valve is designed for continuous flow applications and can be used to meter flow if desired. Each valve is adjustable for a differential pressure of between 1.7 bar and 8.6 bar.
Unless otherwise specified valves are factory set at 2.75 bar.
Flexible drive couplings are used for Smith CO2 pumps whether mounted on steel baseframes with motors or engines or for pumps mounted directly onto electric motors.
Recommended couplings consist of two metal flanges and one flexible rubber vibration damping insert disc. Custom sized bores for metric and unusual motor shaft sizes can be supplied on request.
With a maximum allowable working pressure of 34 bar the Smith strainer is perfectly suited to remove particulate matter in the inlet of Smith CO2 pumps. Improved safety and reduced costs can be achieved by the use of strainers with reducing sizes eliminating extra fittings or bushings.
The screen is very easy to replace due to the exclusive narrow guide vane and a taper in the strainer body. The screen glides easily into position preventing breakage or buckling which otherwise could allow foreign matter to pass through. The reinforced mesh screen provides superior efficiency compared with inferior perforated metal screens. Screens are available in either brass 40 mesh or 300 series stainless steel 80 mesh.