volumetric efficiency hydraulic pump manufacturer

In a condition-based maintenance environment, the decision to change out a hydraulic pump or motor is usually based on remaining bearing life or deteriorating efficiency, whichever occurs first.

Despite recent advances in predictive maintenance technologies, the maintenance professional’s ability to determine the remaining bearing life of a pump or motor, with a high degree of accuracy, remains elusive.

Deteriorating efficiency on the other hand is easy to detect, because it typically shows itself through increased cycle times. In other words, the machine slows down. When this occurs, quantification of the efficiency loss isn’t always necessary. If the machine slows to the point where its cycle time is unacceptably slow, the pump or motor is replaced. End of story.

In certain situations, however, it can be helpful, even necessary, to quantify the pump or motor’s actual efficiency and compare it to the component’s native efficiency. For this, an understanding of hydraulic pump and motor efficiency ratings is essential.

There are three categories of efficiency used to describe hydraulic pumps (and motors): volumetric efficiency, mechanical/hydraulic efficiency and overall efficiency.

Volumetric efficiency is determined by dividing the actual flow delivered by a pump at a given pressure by its theoretical flow. Theoreticalflow is calculated by multiplying the pump’s displacement per revolution by its driven speed. So if the pump has a displacement of 100 cc/rev and is being driven at 1000 RPM, its theoretical flow is 100 liters/minute.

Actualflow has to be measured using a flow meter. If when tested, the above pump had an actual flow of 90 liters/minute at 207 bar (3000 PSI), we can say the pump has a volumetric efficiency of 90% at 207 bar (90 / 100 x 100 = 90%).

Its volumetric efficiency used most in the field to determine the condition of a hydraulic pump - based on its increase in internal leakage through wear or damage. But without reference to theoretical flow, the actual flow measured by the flow meter would be meaningless.

A pump’s mechanical/hydraulic efficiency is determined by dividing thetheoretical torque required to drive it by the actual torque required to drive it. A mechanical/hydraulic efficiency of 100 percent would mean if the pump was delivering flow at zero pressure, no force or torque would be required to drive it. Intuitively, we know this is not possible, due to mechanical and fluid friction.

Table 1. The typical overall efficiencies of hydraulic pumps, as shown above, are simply the product of volumetric and mechanical/hydraulic efficiency.Source: Bosch Rexroth

Like theoretical flow, theoretical drive torque can be calculated. For the above pump, in SI units: 100 cc/rev x 207 bar / 20 x p = 329 Newton meters. But like actual flow, actual drive torque must be measured and this requires the use of a dynamometer. Not something we can - or need - to do in the field. For the purposes of this example though, assume the actual drive torque was 360 Nm. Mechanical efficiency would be 91% (329 / 360 x 100 = 91%).

Overall efficiency is simply the product of volumetric and mechanical/hydraulic efficiency. Continuing with the above example, the overall efficiency of the pump is 0.9 x 0.91 x 100 = 82%. Typical overall efficiencies for different types of hydraulic pumps are shown in the Table 1.

System designers use the pump manufacturers’ volumetric efficiency value to calculate the actual flow a pump of a given displacement, operating at a particular pressure, will deliver.

As already mentioned, volumetric efficiency is used in the field to assess the condition of a pump, based on the increase in internal leakage due to wear or damage.

When calculating volumetric efficiency based on actual flow testing, it’s important to be aware that the various leakage paths within the pump are usually constant. This means if pump flow is tested at less than full displacement (or maximum RPM) this will skew the calculated efficiency - unless leakage is treated as a constant and a necessary adjustment made.

For example, consider a variable displacement pump with a maximum flow rate of 100 liters/minute. If it was flow tested at full displacement and the measured flow rate was 90 liters/minute, the calculated volumetric efficiency would be 90 percent (90/100 x 100). But if the same pump was flow tested at the same pressure and oil temperature but at half displacement (50 L/min), the leakage losses would still be 10 liters/minute, and so the calculated volumetric efficiency would be 80 percent (40/50 x 100).

The second calculation is not actually wrong, but it requires qualification: this pump is 80 percent efficient at half displacement. Because the leakage losses of 10 liters/minute are nearly constant, the same pump tested under the same conditions will be 90 percent efficient at 100 percent displacement (100 L/min) - and 0 percent efficient at 10 percent displacement (10 L/min).

To help understand why pump leakage at a given pressure and temperature is virtually constant, think of the various leakage paths as fixed orifices. The rate of flow through an orifice is dependant on the diameter (and shape) of the orifice, the pressure drop across it and fluid viscosity. This means that if these variables remain constant, the rate of internal leakage remains constant, independent of the pump"s displacement or shaft speed.

Overall efficiency is used to calculate the drive power required by a pump at a given flow and pressure. For example, using the overall efficiencies from the table above, let us calculate the required drive power for an external gear pump and a bent axis piston pump at a flow of 90 liters/minute at 207 bar:

As you’d expect, the more efficient pump requires less drive power for the same output flow and pressure. With a little more math, we can quickly calculate the heat load of each pump:

No surprise that a system with gear pumps and motors requires a bigger heat exchanger than an equivalent (all other things equal) system comprising piston pumps and motors.

Hydraulic systems are in general members of the fluid power branch of power transmission. Hydraulic pumps are also members of the hydraulic power pack/hydraulic power unit family. Hydraulic units are encased mechanical systems that use liquids for hydraulics.

The hydraulic systems that hydraulic pumps support exist in a range of industries, among them agriculture, automotive manufacturing, defense contracting, excavation, and industrial manufacturing. Within these industries, machines and applications that rely on hydraulic pumps include airplane flaps, elevators, cranes, automotive lifts, shock absorbers, automotive brakes, garage jacks, off-highway equipment, log splitters, offshore equipment, hydraulic motors/hydraulic pump motors, and a wide range of other hydraulic equipment.

When designing hydraulic pumps, manufacturers have many options from which to choose in terms of material composition. Most commonly, they make the body of the pump–the gears, pistons, and hydraulic cylinders–from a durable metal material. This metal is one that that can hold up against the erosive and potentially corrosive properties of hydraulic fluids, as well as the wear that comes along with continual pumping. Metals like this include, among others, steel, stainless steel, and aluminum.

First, what are operating specifications of their customer? They must make sure that the pump they design matches customer requirements in terms of capabilities. These capabilities include maximum fluid flow, minimum and maximum operating pressure, horsepower, and operating speeds. Also, based on application specifications, some suppliers may choose to include discharge sensors or another means of monitoring the wellbeing of their hydraulic system.

Next, what is the nature of the space in which the pump will work? Based on the answer to this question, manufacturers will design the pump with a specific weight, rod extension capability, diameter, length, and power source.

Manufacturers must also find out what type of substance does the customer plan on running through the pumps. If the application calls for it, manufacturers can recommend operators add other substances to them in order to decrease the corrosive nature of certain hydraulic fluids. Examples of such fluids include esters, butanol, pump oils, glycols, water, or corrosive inhibitors. These substances differ in operating temperature, flash point, and viscosity, so they must be chosen with care.

All hydraulic pumps are composed in the same basic way. First, they have a reservoir, which is the section of the pump that houses stationary fluid. Next, they use hydraulic hoses or tubes to transfer this fluid into the hydraulic cylinder, which is the main body of the hydraulic system. Inside the cylinder, or cylinders, are two hydraulic valves and one or more pistons or gear systems. One valve is located at each end; they are called the intake check/inlet valve and the discharge check/outlet valve, respectively.

Hydraulic pumps operate under the principle of Pascal’s Law, which states the increase in pressure at one point of an enclosed liquid in equilibrium is equally transferred to all other points of said liquid.

To start, the check valve is closed, making it a normally closed (NC) valve. When the check is closed, fluid pressure builds. The piston forces the valves open and closes repeatedly at variable speeds, increasing pressure in the cylinder until it builds up enough to force the fluid through the discharge valve. In this way, the pump delivers sufficient force and energy to the attached equipment or machinery to move the target load.

When the fluid becomes pressurized enough, the piston withdraws long enough to allow the open check valve to create a vacuum that pulls in hydraulic fluid from the reservoir. From the reservoir, the pressurized fluid moves into the cylinder through the inlet. Inside the cylinder, the fluid picks up more force, which it carries over into the hydraulic system, where it is released through the outlet.

Piston pumps create positive displacement and build pressure using pistons. Piston pumps may be further divided into radial piston pumps and axial piston pumps.

Radial pumps are mostly used to power relatively small flows and very high-pressure applications. They use pistons arranged around a floating center shaft or ring, which can be moved by a control lever, causing eccentricity and the potential for both inward and outward movement.

Axial pumps, on the other hand, only allow linear motion. Despite this, they are very popular, being easier and less expensive to produce, as well as more compact in design.

Gear pumps, or hydraulic gear pumps, create pressure not with pistons but with the interlocking of gear teeth. When teeth are meshed together, fluid has to travel around the outside of the gears, where pressure builds.

External gear pumps facilitate flow by enlisting two identical gears that rotate against each other. As liquid flows in, it is trapped by the teeth and forced around them. It sits, stuck in the cavities between the teeth and the casing, until it is so pressurized by the meshing of the gears that it is forced to the outlet port.

Internal gear pumps, on the other hand, use bi-rotational gears. To begin the pressurizing process, gear pumps first pull in liquid via a suction port between the teeth of the exterior gear, called the rotor, and the teeth of the interior gear, called the idler. From here, liquid travels between the teeth, where they are divided within them. The teeth continue to rotate and mesh, both creating locked pockets of liquid and forming a seal between the suction port and the discharge port. Liquid is discharged and power is transported once the pump head is flooded. Internal gears are quite versatile, usable with a wide variety of fluids, not only including fuel oils and solvents, but also thick liquids like chocolate, asphalt, and adhesives.

Various other types of hydraulic pumps include rotary vane pumps, centrifugal pumps, electric hydraulic pumps, hydraulic clutch pumps, hydraulic plunger pumps, hydraulic water pumps, hydraulic ram pumps, portable 12V hydraulic pumps, hydraulic hand pumps, and air hydraulic pumps.

Rotary vane pumps are fairly high efficiency pumps, though they are not considered high pressure pumps. Vane pumps, which are a type of positive-displacement pump, apply constant but adjustable pressure.

Centrifugal pumps use hydrodynamic energy to move fluids. They feature a rotating axis, an impeller, and a casing or diffuser. Most often, operators use them for applications such as petroleum pumping, sewage, petrochemical pumping, and water turbine functioning.

Electric hydraulic pumps are hydraulic pumps powered by an electric motor. Usually, the hydraulic pump and motor work by turning mechanisms like impellers in order to create pressure differentials, which in turn generate fluid movement. Nearly any type of hydraulic pump can be run with electricity. Most often, operators use them with industrial machinery.

Hydraulic clutch pumps help users engage and disengage vehicle clutch systems. They do so by applying the right pressure for coupling or decoupling shafts in the clutch system. Coupled shafts allow drivers to accelerate, while decoupled shafts allow drivers to decelerate or shift gears.

Hydraulic ram pumps are a type of hydraulic pump designed to harness hydropower, or the power of water, to elevate it. Featuring only two moving hydraulic parts, hydraulic ram pumps require only the momentum of water to work. Operators use hydraulic ram pumps to move water in industries like manufacturing, waste management and sewage, engineering, plumbing, and agriculture. While hydraulic ram pumps return only about 10% of the water they receive, they are widely used in developing countries because they do not require fuel or electricity.

Hydraulic water pumps are any hydraulic pumps used to transfer water. Usually, hydraulic water pumps only require a little bit of energy in the beginning, as the movement and weight of water generate a large amount of usable pressure.

Air hydraulic pumps are hydraulic pumps powered by air compressors. In essence, these energy efficient pumps work by converting air pressure into hydraulic pressure.

Hydraulic pumps are useful for many reasons. First, they are simple. Simple machines are always an advantage because they are less likely to break and easier to repair if they do. Second, because fluid is easy to compress and so quick to create pressure force, hydraulic pumps are very efficient. Next, hydraulic pumps are compact, which means they are easy to fit into small and oddly shaped spaces. This is especially true in comparison to mechanical pumps and electrical pumps, which manufacturers cannot design so compactly. Speaking of design, another asset of hydraulic pumps is their customizability. Manufacturers can modify them easily. Likewise, hydraulic pumps are very versatile, not only because they are customizable, but also because they can work in places where other types of pump systems can’t, such as in the ocean. Furthermore, hydraulic pumps can produce far more power than similarly sized electrical pumps. Finally, these very durable hydraulic components are much less likely to explode than some other types of components.

To make sure that your hydraulic pumps stay useful for a long time, you need to treat them with care. Care includes checking them on a regular basis for problems like insufficient fluid pressure, leaks, and wear and tear. You can use diagnostic technology like discharge sensors to help you with detect failures and measure discharge pressure. Checking vibration signals alone is often not enough.

To keep yourself and your workers safe, you need to always take the proper precautions when operating or performing maintenance and repairs on your hydraulic pumps. For example, you should never make direct contact with hydraulic fluid. For one, the fluid made be corrosive and dangerous to your skin. For two, even if the pump isn’t active at that moment, the fluid can still be pressurized and may potentially harm you if something goes wrong. For more tips on hydraulic pump care and operation, talk to both your supplier and OSHA (Occupational Safety and Health Administration).

Pumps that meet operating standards are the foundation of safe and effective operations, no matter the application. Find out what operating standards your hydraulic pumps should meet by talking to your industry leaders.

The highest quality hydraulic pumps come from the highest quality hydraulic pump manufacturers. Finding the highest quality hydraulic pump manufacturers can be hard, which is why we have we listed out some of our favorites on this page. All of those whom we have listed come highly recommended with years of experience. Find their information nestled in between these information paragraphs.

Once you have put together you list, get to browsing. Pick out three or four hydraulic pump supply companies to which you’d like to speak, then reach out to each of them. After you’ve spoken with representatives from each company, decide which one will best serve you, and get started on your project.

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Hydraulics are essential in many industrial applications; they use mechanical energy to force liquid into a system. Within the category of hydraulics, there are many different types of hydraulic pumps that accomplish various tasks within industrial fields. Let’s take a look at some of them.

An axial piston hydraulic pump is also a positive displacement pump. Axion pumps have cylinders that are assembled around a central axis (cylinder block). Within each cylinder, there are pistons which will attach to a swashplate or wobble plate. These swashplates then connect to the rotating shaft, which moves the pistons and pulls them in and out of the cylinders.

Axial piston pumps can also be made into variable displacement piston pumps, which provide more control over speed. In variable pumps, the swashplate is used to set the depth of the pistons, which creates a length variation to affect the discharge volume. This design helps maintain constant discharge rates in industrial applications.

Another hydraulic pump type is the radial piston pump. As the name suggests, the pistons are arranged along the radius of the cylindrical block, which includes the pintle and rotor. The rotor powers the pistons through the cylinders and forces hydraulic fluid in and out of the cylinder.

Both axial and radial piston pumps are used for high-operating pressures as they can withstand much higher pressures than hydraulic pump types. They are often used in ice and snow control applications, as well as on truck-mounted cranes.

A rotary vane pump is also a type of positive displacement pump. It uses rigid vanes rather than the rotor hubs. These vanes are placed around an eccentric rotor device, which moves around the inside wall of the housing container. This movement forces the hydraulic fluid through the discharge port, and, in some applications, can be adjusted to align with the rotational axis of the motor.

Vane pumps are often used in utility vehicles but have lost popularity over the years in favor of gear pump hydraulic systems. However, they used to be very common in aerial buckets and ladders along with other mobile, truck-mounted hydraulic applications.

Gear pumps have become the most common hydraulic pump type that’s used in industrial applications today. The gear pump has fewer moving parts than piston or vane pumps, which makes it easy to service and relatively inexpensive compared to other hydraulic pumps. They are also less likely to be contaminated during use.

An external gear pump uses two gears on the outside of individual shafts to aid in movement and push both thin and thick fluids through the gears. These external pumps are commonly used in fixed-displacement applications and high-pressure environments.

Internal gear pumps place gears on the insides of the shafts rather than on the outside as found in external gear pumps. That makes them self-priming and non-pulsing, and can even be run without liquid for short periods of time—although they can’t be left dry for too long.

Additionally, internal gear pumps are bi-rotational, meaning that one can be utilized to both unload and load devices. And, with only two moving parts, they are considered to be one of the most reliable types of hydraulic pumps.

Volumetric efficiency is the amount of output the pump actually produces as a percentage of its theoretical production.The higher the percentage the more efficient the pump.

Among the factors affecting volumetric efficiency are leakage and fluid compressibility (ability for volume to be reduced under pressure). These issues can cause the pump to lose efficiency and waste energy as that energy converts to heat.

Still have questions about hydraulic pumps or their parts and repairs? Contact Panagon Systems today. We’ve been a leading hydraulic pump manufacturer in the U.S. for over two decades, and can help you find the best solution for your application. You can view our full line of pumps here. To request a consultation or quote, please fill out our online form.

High-pressure pumps with fixed output per revolution and very high volumetric efficiency up to 98%, belonging to the top of the high-pressure hydraulic sector. Create perfect synchronisation of cylinders or hydraulic motors with the multi-output radial piston pumps, thanks to their very high efficiency.  Due to their bidirectional rotation, these pumps can be used universally. Very wide range of speed allowing variable flow rate. Available in combination with under-oil motor for extremely low-noise set-ups.

Volumetric efficiency is the actual amount of fluid flowing through a pump, rather than its theoretical maximum. Put another way, it is the measure of volumetric losses of a reciprocal pump through internal leakage and fluid compression; this calculation is the value that should be used to evaluate your current pumping mechanism.

Common causes of loss in volumetric efficiency include worn valves, seats, liners, piston rings, or plungers, pockets of air or vapor in the inlet line or trapped above the inlet manifold, or loose belts, valve covers, cylinder heads, or bolts in the pump inlet manifold. Routine maintenance and inspection in these areas can greatly increase output over time.

Obstructions such as a safety relief valve partially held open or failing to maintain pressure, foreign objects preventing the pump inlet or discharge valve from closing or blocking liquid passage, or a vortex in the supply tank are some of the other more easily remedied factors reducing efficiency.

There are many potential hazards that can hamper volumetric efficiency and cause your components to operate at less than full strength — but there are also a number of methods to increase it.

Volumetric efficiency accounts for the leakage of fluid in the pump that doesn"t do any work.  Mechanical/hydraulic efficiency accounts for friction losses.  Total efficiency is volumetric efficiency X mechanical/hydraulic efficiency.

Depending on what you"re calculating, one of these efficiencies will be important.  For flow rate and speed, volumetric efficiency is important.  For displacement, pressure rise, and torque, mechanical efficiency is important.  Finally, for input power, total efficiency is important.

Before purchasing just any type of pump, it’s essential to have some understanding of both the volumetric and mechanical efficiency of pumps. Of course, when working with a reputable source, a company representative will gladly provide whatever information you need. However, it’s still a good idea to build your knowledge base ahead of time.

For the efficiency of centrifugal pumps, there are four distinct kinds. Along with volumetric and mechanical efficiencies, you should also learn the basics of the hydraulic and overall efficiencies. In layman’s terms, these formulas, whether for multistate centrifugal pumps or centrifugal vacuum pumps, ensure the most efficient operation possible.

Volumetric Efficiency – The official definition for this particular efficiency is the ratio of the actual flow rate that the pump delivers to the theoretical discharge flow rate. The latter is the flow rate void of any leakage. Typically, you would use this formula to determine the volume of liquid lost during the flow because of a leak.

Mechanical Efficiency – For the various types, including centrifugal vacuum pumps and others, the formula for this efficiency is the ratio of theoretical power the pump needs to operate to the actual power delivered to the pump itself. In this case, you would use this efficiency formula to identify power lost in specific moving parts such as the bearings. Ultimately, mechanical efficiency determines the amount of power a pump must have to perform optimally.

Hydraulic Efficiency – The mechanical energy of multistate centrifugal pumps and other types converts into hydraulic energy. This consists of flow, pressure, and velocity. The ratio formula for hydraulic efficiency is useful hydrodynamic energy in the form of fluid to the amount of mechanical energy delivered to the rotor. Smaller centrifugal pumps usually land in the 50 to 70 percent range. In comparison, larger ones typically reach efficiencies of 75 to 93 percent.

Overall Efficiency – The ratio formula for this is the output of actual power of centrifugal pumps to the input of actual power. The overall efficiency is what you would rely on to determine the amount of energy lost overall.

Whether you’re in the market for one of the types of centrifugal pumps mentioned or you already have one that needs servicing, you can always count on the experts at PFS Pumps. With years of experience in both areas, we guarantee quality and affordability. Contact us today for more information.

Gear pumps are often used in pumping relatively viscous liquids, such as some viscous liquid hydrocarbons, liquid fuels, lubrication oil pumping in machinery packages, hydraulic units and fluid power transfer units. Gear pumps are the most popular type of positive displacement pump. Small gear pumps usually operate at a speed between 1,700 rpm and 4,500 rpm, and larger models most often operate at speeds below 1,000 rpm.

A gear pump produces flow by carrying fluid between the teeth of two meshing gears. The chambers formed between adjacent gear teeth are enclosed by the pump housing and side plates, also called wear or pressure plates. A partial vacuum is created at the pump suction; fluid flows in to fill the space and is carried around the discharge of the gears. As the teeth mesh at the discharge end, the fluid is forced out. Volumetric efficiencies of gear pumps run as high as 91 percent.

Gear pumps have close tolerances and shaft support, usually on both sides of the gears. This allows them to run to pressures beyond 200 bar gauge (Barg), making them well suited for use in high-pressure applications. With bearings in the liquid and tight tolerances, gear pumps are not usually well suited to handle abrasive or extremely high temperature applications.

Tighter internal clearances provide for a reliable measure of liquid passing through a pump and for greater flow control. Because of this, gear pumps might be employed for some precise transfer and metering applications.

During the past few decades, a large number of pump concepts have emerged, and the selection of an appropriate pump for a specific viscous liquid application has become a major consideration. In general, a specific pump can be operated efficiently for one application but might be inappropriate for others. To aid the selection and design of pumps, different charts and tables have been developed to illustrate the efficiencies and performance of various pump types as a function of the specific speed and other parameters. In addition to these theoretical concepts of efficiencies and suitability of pressure ranges, other important benefits such as reliability, availability, overall performance and operation should be respected. Among positive displacement pumps, gear pumps possess some vital advantages.

The gear pump principle features low-pressure pulsations due to the large number of tooth gaps conveying the fluid, which leads to excellent suction behavior and helps prevent cavitation.

Various pressure compensation measures and characteristics of gear pumps can offer desirable differential pressure and flow characteristics curve for many applications, and gear pumps can also offer high efficiencies for many targeted services.

Employing an appropriate combination of self-lubricating materials, a gear pump can be safely operated even when gas bubbles are trapped in the flow subsequent to cavitation phenomena.

As the gears come out of mesh, they create expanding volume on the suction side of a gear pump. Liquid flows into the gear teeth cavity and is trapped by the gear teeth as they rotate. Liquid could also travel around the interior of the casing in the pockets between the teeth and the casing. This small flow does not pass between the gears. The meshing of gears forces liquid through the discharge port under pressure.

In gear pumps, running clearances between gear faces, gear tooth crests and the housing creates a relatively constant loss in any pumped volume at a fixed pressure. This means that volumetric efficiency at low speeds and low flows might be poor, so gear pumps should be run close to their maximum rated speeds.

Many pumping applications of viscous liquids require adjusted flow independent of discharge pressure and also pressure-independent volumetric efficiency. Some gear pumps consist of a pressure-compensating sealing element that can reduce the face and tip clearances to decrease the internal leakage and increase the volumetric efficiency. The design of the sealing elements is usually based on theoretical predictions combined with practical experience. The seal’s geometry and designs should be optimized in several stages. Operational experience with gear pumps using properly designed pressure-compensating sealing elements has shown that when a critical differential pressure (say around 6-10 Barg) is exceeded, the desirable characteristics and an almost pressure-independent volumetric efficiency around 74 to 88 percent could be achieved.

Moreover, the pressure pulsations induced by the unsteady discharge of a gear pump should be measured to verify trouble-free operation of a gear pump. Pressure pulsations or ripples (suction or discharge) can arise from an interaction of the pumping dynamics with the dynamic behavior of the suction and discharge piping system. The presence of pressure pulsation would lead to a fluctuating pressure differential, and hence a fluctuating flow into the gear inter-tooth space. If the minimum pressure pulsation points coincide with the expansion phase as the side flow areas open up, it might result in some malfunctions or poor performance.

In a gear pump, the friction torque and consequent pump operation and required power can be affected by liquid temperature as well as operating pressure and pump speed. When the pressure differential is large, the friction torque decreases first and then increases with an increase in pump speed. For a large pressure differential, the friction torque could become higher with an increase in liquid temperature in a low pump speed region, but it could have the opposite tendency in a high pump speed region.

When a gear pump operates with a relatively low suction pressure (for instance, when liquid is from a tank at a lower level), pressures in the suction piping and chamber get closer to vapor pressure, and cavitation can take place upstream from the gear meshing region.

To study the effects of operation parameters such as suction pressure on pump operation, in a case study a gear pump has been operated at 1,200 rpm and 3,400 rpm speeds with around 20 Barg discharge pressure. The pump suction is from an atmospheric tank. An 0.8 bar pressure drop in the suction was observed when pump was operated at 3,400 rpm. In other words, at around 3,400 rpm, the gear pump should be operated with a mean suction absolute pressure of 0.2 bar absolute (Bara), which is relatively close to the pump limit, and cavitation should be expected. At 1,500 rpm, this same situation represented a smaller suction pressure drop of only about 0.5 bar; this resulted in a mean suction absolute pressure of approximately 0.5 Bara with some good margin against cavitation.

Gear pumps can usually come in single or double (two sets of gears) pump configurations with different types of gear such as spur, helical, herringbone gears. Helical and herringbone gears typically offer a smoother flow compared to spur gears, although all gear types are relatively smooth. Straight spur gears are easiest to cut and are the most widely used. Helical and herringbone gears run more quietly but cost more. They are typically used in large capacity gear pumps.

Displacement volumes of a gear pump are directly affected by the gear tooth profile. Since the involute gear tooth profile is easily manufactured and the technology for the power transmission gear can be applied, this profile is usually adopted for a low cost gear pump. In an involute gear, the profiles of the teeth are involutes of a circle.

Many gear pumps use helical gears. The teeth on helical gears are cut at an angle to the face of the gear. When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement. This gradual engagement makes helical gears operate more smoothly and quietly than spur gears. Because of the angle of the teeth on helical gears, a thrust load (axial load) is created on the gear when they mesh.

This load should be properly addressed, for example, by using thrust (axial) bearings. The use of helical gears is indicated when the application involves relatively high speeds, relatively high power pumps or where noise abatement is important.