2 `DH` SERIES GENERAL DESCRIPTION The oil pump is a vital part of any oil fired heating plant, whether being used as a transfer pump for pumping oil at low pressures or on an oil burner delivering oil at 35 bar. The Dunphy DH series pump has been specifically designed to overcome the problems associated with current grades of fuel oils in a variety of different situations, giving accurate pressure control combined with reliability and performance. The pump housing is Grade 14 cast iron that is precision machined to accept the various combinations of gear sets that are available to suit a wide variety of applications. Exhaustive work on test rig and field trials that internal leakage s in a gear pump are most severe through the lateral running clearances. They are less severe through the radial clearances, here, the leakage path is long and the rotation of the gears opposes the pressure gradient. Based on these observations a `Sandwich` construction of the gear-set and the pumping chamber has been designed from first principles. Calculations and computer modelling gave clear figures for the very high bearing loads resulting from high liquid pressure acting on the projected area of the gears. As a result, the design has catered for bearings of large surface area. This must result in minimal rubbing speed. They must also provide rigid shaft support with no appreciable deflection. The final design provides all DH series with gear-sets of nitrogen hardened steel supported by an extremely strong bearing assembly. It enables the standard unit to handle fuels with viscosities from 2 up to 2000 centistokes at pressures up to 35 bar and temperatures of up to 140ºC. Single or tandem gear-sets can be offered as standard. Pumps with special series gear-sets can be offered for specific applications. The most characteristic and frequent failure of oil pumps is that of pump seizure. In operation, a gear pump is required to deliver the maximum possible volume for a given centre distance and face-width of the gears. Losses due to internal leakage must be minimal and sufficient only to provide adequate lubrication of the rotating parts. However, the capacity of the gear-set depends on the depth of the gear tooth. Design must therefore cater for a minimum number of teeth and for minimum peripheral rubbing speeds These parameters were used in making a choice between an internal pinion and rotor format and an external gear-set employing straight spur gear teeth of corrected involute form. Dunphy engineers chose the external gear-set because it provides maximum capacity for minimum peripheral rubbing speeds. This factor is of vital importance in the elimination of 2
3 PRESSURE REGULATION A pressure regulating valve is provided as a standard feature of the pump. It is located within the pump body and consists of a steel piston with P.T.F.E. wipers that slides in a honed steel bore. Pressure is exerted on the piston itself by a spring, the loading of which is adjustable by the user. The pressure of the oil bears on the cross sectional area of the piston. When oil pressure and spring force balance, the piston lifts and permits by-passed oil to return to the suction port. The accuracy of the machining and honing ensures that the close fitting piston is kept in contact with the cylinder bore by the pressure of oil acting on its annular area This combination of material selection and fine tolerance eliminates edge filtration, prevents sticking in operation and reduces hysteresis effects to an absolute minimum. The Dunphy DH Series of oil pumps has been purposefully designed, in-house, to a demanding brief, by experienced engineers who have learned, at plant level, what qualities the user demands of an oil pump. As a result the DH oil pump has been designed up to an extremely high quality standard. For heavy oil installations, the DH pump can be fitted with a restrictor which will allow oil from the ring main system to circulate through the flexible oil lines and also the pump body when the burner is not running. This facility eliminates the need to insulate the pump and the flexibles and ensures that both are kept at the correct temperature. Dunphy pump and valve cluster with DH series pump 3
4 TECHNICAL DATA SUMMARY Pump Model Code DHO-1 DH1-1 DH1-2 DH2-1 DH2-2 Gearwheel Capacity litres/hr Gearwheel Capacity gall/hr Weight - kgs Shaft Diameter - mm Fuel Types C up to C Speed 3600 Revolutions per minute ( maximum ) Operating Pressures 35 bar on standard units, maximum of 60 bar on tandem units Capacity Range 145 to 4500 litres/hour ( 32 to 1000 imp gallons/hour approx ) Inlet Pressure 2 bar ( maximum ) ( 30 lbs. sq. inch ) Pump Fixing Flange or Boss Maximum Operating Temperature ( Fuel Oil ) 140 C NOTES 1. PUMP CAPACITY A number of variants can be offered. There are two basic gear-sets available in the range, these cover swept volumes from 290 to 4500 litres/hour at 2 pole ( 2850 rpm and 3400 rpm ) speed. Because running clearances in the pump are at an absolute minimum, the Volumetric Efficiency of the gear-set becomes a function of the viscosity of the liquid being pumped. ( See diagram below ). The further variants arise from the potential of using the pumps as SINGLE, SERIES or TANDEM sets as described in the diagrams below. VOLUMETRIC EFFICIENCY 70% 95% SINGLE SINGLE gear-set VISCOSITY 2. CAPACITIES Capacities are given for pumps running at 2 pole speed ( 2850 rpm ) and a 50 Hz electric supply. SERIES 3. GEARWHEEL CAPACITIES As stated, these give the full swept volume of the pump. The SERIES arrangement provides a similar CAPACITY to the SINGLE but the PRESSURE can be doubled without any increase on the bearing load. TANDEM The TANDEM arrangement DOUBLES the capacity of the SINGLE gear-set. 4 `DH` Series pump fitted to Dunphy light oil burner.
5 Dunphy Branch Offices Worldwide GERMANY Dunphy Feuerungsanlagentechnik Eichenweg GRÜNKRAUT Tel: (49) Mobile: (49) Fax: (49) SPAIN Dunphy Combustion SA C/Juan XXIII No. 7 bajos St. Feliu de Llobregat BARCELONA Tel: (34) Fax: (34) NETHERLANDS Dunphy Benelux BV De Barch 4, 3155 BB MAASLAND Tel: (31) Fax: (31) SWEDEN DCL Combustion AB Poppelvägen SJOBO Tel: (46) Fax: (46) DUNPHY COMBUSTION LTD QUEENSWAY ROCHDALE ENGLAND OL11 2SL Tel +44 (0) Fax: +44 (0) Internet