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What Is High Pressure? [ ]
Cat Pumps is a specialist manufacturer and supplier of high-pressure pumps. But ‘high’ is a subjective term, which means different things to different people. We use ‘high pressure’ to describe a pressure above the capabilities of most common roto-dynamic (centrifugal) pumps, typically we serve applications from 20 up to 400 bar.
High Pressure Pump Design []
 All Cat pumps are positive-displacement reciprocating pumps. A positive-displacement pump is one which takes in a fixed volume of liquid on each inlet stroke and physically moves it through and out of the pump with virtually no losses or inefficiencies. This contrasts with a roto-dynamic pump (e.g. centrifugal pump) which relies on inertia to impart flow or a rotary (semi-) positive pump e.g. a vane or gear pump which can lose flow though internal clearances.
 Most Cat pumps have three synchronised pistons or plungers, which produce a low-pulsation flow, that is sufficiently smooth for most applications, having a slight ripple of maximum 20% peak to peak. Fitting a suitable Pulsation Dampener (accessories) can reduce this to +/- 2.5%. The flow from a Cat pump is highly stable and predictable as the flow rate is determined almost exactly by the running speed of the pump and is virtually unaffected by back-pressure, liquid viscosity or specific gravity.
 The drive-end or rear end of a Cat pump features a heavy-duty chrome-molybdenum crankshaft precisely aligned and supported in high-capacity rolling-element bearings within a precision die-cast alloy crankcase. This crankshaft drives high strength connecting rods pinned to the plunger push-rods. These are accurately aligned within bores in the crankcase to maximise support, minimise wear and to ensure precise concentricity of the pump seals. All the rotating and sliding contact parts of a Cat pump are inside the crankcase, well away from the pumped fluid, and are splash-lubricated by the oil it contains. Our pumps provide optimum life and withstand the most punishing applications, repeated cycles and continuous-duty operation. This heavy-duty industrial quality is evidenced in pumps that were installed 20-30 years ago and are still running today.
Piston and Plunger Pumps []
All Cat pumps are either Piston Pumps or Plunger Pumps. The technical difference between these two similar pump types relates to the seals:
Piston Pump – the high-pressure seal reciprocates with the piston and slides though a smooth-bore cylinder
Plunger Pump – the high-pressure seal is stationary and a smooth cylindrical plunger slides though the seal
A Piston pump copes well with poor inlet conditions e.g. suction lift or a liquid close to its vapour pressure. The mechanically-actuated inlet valves and UNIFLOW design provide an excellent fluid flow path through the pump with strong suction capabilities. For negative inlet head (suction lift) applications, the Flat Valve option also offers additional valve seating for stronger suction. Piston pumps are best suited to applications requiring medium pressures up to 85 bar.
A Plunger pump is better suited to higher pressures. Cat Pumps Plunger pumps feature highly-polished smooth ceramic plungers and uniquely supported high-pressure seals. The precise concentricity of the plungers ensures that they do not impart side loads to the seals, maximising life and durability.
Construction and Materials []
 The liquid-contact head of a Cat Pumps plunger pump is made up of one or two manifolds. Usually these are precision machined from high-quality castings, offering a balance of quality, best manufacturing cost and long life. Cat plunger pumps are available in a choice of liquid-contact materials including Brass, Gunmetal, 316 Stainless Steel and Nickel Aluminium Bronze. This ensures that the best combination of chemical resistance, life cycle costs and initial purchasing economy can always be achieved.
In more demanding applications where excellent chemical resistance is paramount, we supply Block Style pumps. Their manifolds are accurately machined from solid forged billets of material guaranteeing best possible metallurgy, close grain structure, enhanced fatigue strength and resistance to attack from aggressive liquids such as deionised water, demineralised water and high-salinity seawaters. This method of manufacture also minimises the possibility of porosity and inclusions and allows us to offer fully traceable material certification and controlled internal surface finishes. It also extends our range of materials to include Duplex- and Super-Duplex Stainless Steels, Hastelloy™ and Titanium.
Cat Pumps Piston pumps are supplied with either brass or 316 grade stainless steel manifolds and with chrome-plated 304 grade cylinders, sleeves and valves. Piston pumps have been providing dependable service in car wash and central cleaning systems for 35 years.
Seal Design and Selection []
The service life of any pump is determined partly by the life of its seals so correct seal design and selection are vital to the durability of a Cat Pump.
The only sliding surfaces inside the head of a Cat Pumps reciprocating pump are the seals and we offer a unique seal design and exclusive material blends; seals are available in a variety of elastomeric materials ensuring best possible chemical compatibility. We are the only reciprocating, positive displacement pump manufacturer to offer genuine Cat Pumps concentric, solid ceramic plungers. Their high density polished surface greatly enhances seal life. No other pump company goes this far to maximise seal life.
 The pumped fluid provides a microscopic film of liquid to protect and cool the seals and plungers (or pistons). Inevitably, this results a small amount of fluid passing across the main high-pressure (HP) seal from the high pressure side to the low pressure side. Pump seals should be considered to be a normal service item just like the tyres on a car; in a Cat pump, seal deterioration is seen first as a gradual reduction in pump performance facilitating prediction of seal life and allowing a routine seal change to be planned.
To reduce potential external leakage all our pumps have a double seal arrangement with secondary Low Pressure (LP) seals located on the atmospheric side of the HP seals. These trap the small amount of liquid that passes the main HP seals and returns it to the incoming fluid stream, virtually eliminating external leakage. These secondary seals are only required to seal the differential between the inlet pressure and the atmospheric pressure, vastly increasing the life of these components. Extensive research, design and development has lead to our exclusive spring reinforced, special lipped LP seal offering 3-4 times longer life than other seals.
Where the pumped liquid does not have sufficient inherent lubricity for the seals to function e.g. ultra-pure water and liquefied gases, a double seal arrangement can be configured to allow a compatible liquid to be circulated between the HP and LP seals. Special ‘K’ versions of our industrial block-style reciprocating pumps feature a ported inlet manifold permitting flushing of the seals. This provides both lubrication and cooling in high-temperature applications or when containment of emissions is critical. This also allows for seal condition monitoring and dry-run protection assuring a safe work environment. This feature is also now available on certain cast-manifold pumps.
Pump Selection []
Matching a PD pump flow rate to the application:
The output flow from a Cat pump is determined by running speed, plunger diameter and crankshaft stroke and is virtually unaffected by discharge pressure.
Most pumps are available with a choice of different plunger diameters. In a given pump frame size, a large diameter piston or plunger provides more flow at any given speed. But the pressure acting on the larger area transmits more force to the drive end so working pressure is limited to ‘only’ 70 bar! Smaller diameter pistons or plungers deliver less flow but allow the pump to operate reliably at pressures up to 480 bar as less force is transmitted to the drive end. We can advise the precise pump build configuration and running speed for any application and can offer speed-reducing transmissions and variable-speed drives.
A reduced stroke crankshaft is sometimes fitted to reduce flow rate making it easier to control very low flows, or to match the output flow to a fixed running speed e.g. a petrol or diesel engine, direct drive electric motor or drive from machine lay shaft.
Pump discharge pressure:
Cat pumps are often used to pump liquids through spray jets, nozzles and restrictions such as small pipes. It is important to remember that the pump does not cause the pressure. The pump creates a liquid flow and the pressure is a result of restrictions downstream. The pump then generates a pressure sufficient to overcome the restriction; if there is less restriction, the pump generates less pressure. If the reading on a pressure gauge fitted to the system is lower than the maximum pressure rating of the pump that does not necessarily mean there is something wrong with the pump. It may simply indicate that the restriction of the system does not require the full pressure capability of the pump.
If the pressure is less than is required e.g. to achieve the correct spray pattern or jet distance from a nozzle, use a smaller diameter nozzle or consider increasing the pump speed to increase flow.
Pump Drives []
The power needed to drive a Cat pump is almost exactly proportional to discharge pressure and running speed and therefore flow. A simple calculation from flow rate in litres/minute and pressure in bar gives power to drive pump in kilowatts: ( Flow * Pressure ) / 520 = input power. We can supply pumps with the correct size of motor and transmission for your application.
Variable Speed []
Cat pumps are ideally suited to control by variable speed ‘inverter’ drives. At a given discharge pressure the power to drive the pump varies more-or-less linearly with flow as the output is a linear function of the rpm, closely matching the characteristics of an ‘inverter’ controlled electric motor. A variable-speed drive with closed-loop feedback from a pressure transducer will maintain constant pressure against varying flow demand e.g. multiple trigger-gun cleaning installations.
Servicing []
 A correctly installed Cat pump will run for many years with very little servicing. Provided adequate inlet liquid supply is maintained and the system is protected against over-pressure, a simple preventative maintenance schedule will eliminate many potential problems. This will vary slightly with each pump installation and is affected by various factors such as the duty cycle, chemical compatibility, temperature of the pumped liquid, location, inlet conditions and the accessories fitted in the system. The only routine maintenance normally required is regular changing of the crankcase lubricating oil. Seals will need to be replaced periodically and valves even less often.
 Cat pumps are very easy to service. Our emphasis on high quality components and precision manufacturing in all our piston and plunger pumps results in far less frequent servicing than most pumps. Only common workshop tools are required, making in-field service convenient and user friendly.
Service manuals are available in printed form and on-line as downloadable .pdf files. Parts lists and exploded views in the Data Sheets help to identify the parts and convenient service kits that may be required. Technical Bulletins are also available for identifying product changes and servicing procedures and a DVD is also available detailing the disassembly and re-assembly of each pump.
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Technical 
