prime hydraulic pump free sample
Pump is a machine or mechanical equipment which is required to lift a fluid (liquid, semi-solid, gas, steam etc) from low level to high level or to flow fluid from low pressure area to high pressure area or as a booster in a piping network system. Principally, pump converts mechanical energy of motor into fluid flow energy.
Pump Priming is the process of removing air from the pump and suction line. In this process the pump is been filled with the liquid being pumped and this liquid forces all the air, gas, or vapor contained in the passage ways of pump to escape out. Priming maybe done manually or automatically. Not all pumps require priming but mostly do. There are Self Priming Pumps and also some layout situations where priming is not required. Same will be discussed in this article as it progresses.
Priming a pump is probably the first and one of the most important thing one should do before operating it. Not priming a pump or not doing it properly makes majorityof pump problems. Any problem in pump due to lack of priming may cause financial impact due to pump maintenance and the downtime of piping system due to a malfunctioning pump.
Priming reduces the risk of pump damage during start-up as it prevents the the pump impeller to becomes gas-bound and thus incapable of pumping the desired liquid.
For reliable operation, pumps must first be primed; that is, air or gases to be expelled from the suction and impeller eye area and replaced with liquid to be pumped. The pump would not function properly when not completely filled with liquid. Along with compromised performance, not priming the pump and allowed to run without fluid, it will overheat the pump system and there will be a danger of damage to critical internal pump components.
In principle, all Positive Displacement Pumps are self-priming. In particular, this includes different type of rotary and reciprocating pumps. The priming of Positive Displacement Pump is required only at the time of first starting as under dry running conditions the pump may overheat. But in a Centrifugal Pump (except Self Priming Pump) priming is required in starting after every shutdown.
Centrifugal Pumps are designed to pump liquids not gases. Centrifugal Pump can not suck the liquid, but it pushes the liquid from suction to discharge. Due to pressure difference created by the liquid pushed to the discharge with an additional push on liquid from the atmospheric pressure in the storage tank connected to pump suction piping, more liquid enter in the suction side of pump provided suction line is completely filled with liquid (primed). Its sort of that pushesthe liquid out and pullingeffect is not so prominent. During the start up of the pump if any air pocket is present at the suction side, then pump will push the air. As a result air present in the suction side will try to expand and it will block the liquid from entering into the centrifugal pump.
Also explained in other words, in Centrifugal Pump the head developed (in meters of liquid that is pumped) depends on the velocities determined by diameter of the impeller and the impeller speed (rpm.). As the pressure developed is related to the head by the equation head = pr / sp. weight,the pressure available will be proportional to the specific weight of the liquid. This means that the pressure (or pressure difference) created with air will be only around 1/800 times that with water (density of water = 1000 kg/ m3 and dry air at S.T.P has a density of 1.2 kg/m3 ). Therefore, if the pump is not primed, the suction pressure created will not be sufficient to lift water.
Whereas in Positive Displacement Pump, during suction phase, piston moves backward and form a low pressure zone in the pump. This pressure difference between suction & storage tank is large enough to pull the liquid, even if air pocket is present in the suction line. In short, it creates a high initial vacuum during the start of suction stroke. Positive displacement pumps can evacuate all the air in its cylinder by virtue of its motion and therefore a better pressure (vacuum) is also generated. So we need not have priming operation in positive displacement pumps.
Also a common feature of all Positive Displacement Pumps is the use of close tolerance parts to prevent fluid returning from the discharge to the suction side. Depending on the effectiveness of these seals created by these close-tolerance parts, a positive displacement pump is capable of venting air from its suction to discharge and prevent the vented air from returning back. Whereas in Centrifugal Pumps, the pumping action is generated by the transfer of rotational energy from the impeller to the liquid. There are no seals between the suction and discharge sides of the pump making it ineffective with gases.
With Positive Displacement Pumps, there is a danger of cavitation occurring at the point when liquid starts to enter the pump and there is a liquid/air mixture. Under these conditions, vapor bubbles form and expand on the suction side of the pump. Upon reaching the high pressure, discharge side of the pump, the bubbles collapse violently causing vibration and damage to the pumping elements. For these reasons, it is important to refer to the manufacturer standard and operating procedure before using a positive displacement pump in an application where it must self-prime and, of necessity, be run dry for any period.
However, with a few modifications to the basic design, a centrifugal pump can be made Self Priming. The details of Self Priming Pumps will be discussed in this article later on.
Priming is only not required when the pump is either capable of removing air and gases from itself (also known as Self Priming Pumps) or the layout conditions are so much favorable that the pump will be always completely filled with the liquid to be pumped. Few such conditions are detailed out below.
Priming is not required when the pump is at a lower elevation than the supply and this ensures that pump suction will be completely filled with liquid at all times (known as “Flooded Suction Condition”).
Priming of a pump can be achieved by either layout consideration, or by means of some external arrangements that ensures priming or by use of Self Priming Pumps. Few of the external arrangements that ensures priming of a pump are detailed out below.
In this method of pump priming, liquid is poured in the pump suction. This can be achieved by pouring liquid directly in suction or with the help of other devices like a funnel and the pump will be manually primed with a gravity feed. While priming is being done, all the air escapes through air vent valve.
In this method of pump priming, a small size vacuum pump or self priming pump or a positive displacement pump is being used for priming the main centrifugal pump. The suction line of positive displacement pump is connected to the discharge line of main centrifugal pump. This positive displacement priming pump evacuate all the air in the primary pump and suction piping.
In this method of pump priming, water available at high head is allowed to flow through a nozzle. The nozzle is so designed that at the jet outside the nozzle the pressure is less than the atmospheric pressure so it is possible to suck water from the sump.
In this method of pump priming, air-water separation chamber is provided on the delivery side of pump and a bent suction pipe portion is provided at the inlet of the pump. Bent suction pipe portion always maintain some liquid in the pump. Air is separated and expelled through pump discharge or air vent and liquid, being heavier than air, falls back into separation chamber.
This design is made part of some self priming centrifugal pumps too. In self-priming centrifugal pumps with a separation chamber the fluid pumped and the entrained air bubbles are pumped into the separation chamber by the impeller action. The air escapes through the pump discharge nozzle whilst the fluid drops back down and is once more entrained by the impeller. The suction line is thus continuously evacuated. This design has two major drawbacks. Firstly reduced pump efficiency and secondly large dimensions due to incorporation of separation chamber.
In this method of pump priming, ejector is provided on the suction side of pump. Ejectors operate by creating a vacuum inside the suction line of the pump. The vacuum draws the liquids from sump up to the pump elevation. Ejectors require a Compressed Air Supply as an energy input.
In this method of pump priming, a foot valve (functioning as a NRV) is installed in the suction piping to insure that the liquid will not drain from the pump casing and suction piping once the pump stops operating. A foot valve is a form of check valve installed at the bottom, or foot, of a suction line. When the pump stops and the ports of the foot valve close, the liquid cannot drain back from pump suction if the valve seats tightly. Keep in mind that these foot valves have a nasty habit of leaking.
For prevention of a pump, where priming is required, operation without being primed various methods are being used. The basic of these methods are to trigger some form of alarm or auto shutdown of pump if the pump is not filled with liquid completely. One such scenario is discussed below.
In some pumps, a form of float switch in a chamber connected with the suction line is being used. If the level in the chamber is above the impeller eye of the pump, the float switch control allows the pump to operate. If the liquid falls below a safe level, the float switch acts through the control to stop the pump, to prevent its being started, to sound an alarm, or to light a warning lamp.
Self Priming Pumps are designed to have the ability to prime themselves automatically, when operating under a suction lift, to free themselves of entrained air or gases, and to continue normal pumping without external priming. They can be broken down into three basic types:
Liquid Primed Self Priming Pumps have their own in-built or separate liquid reservoir (known as “Priming Chamber”) that must be filled with liquid in order to “self prime” the pump. Without this initial liquid charge filled in priming chamber, a liquid primed self priming pump will not prime or pump. Liquid primed self priming pump generally operate in an air-liquid mixture by transforming this mixture into a fluid that can be pumped without help of any external auxiliary devices. Priming chamber allows liquid primed self priming pumps to recirculate liquid within the pump at will, ridding the pump of the air that prevents it from operating whenever necessary.
A Liquid Primed Self Priming Pump has two phases of operation: “Priming Mode” and “Pumping Mode”. During priming mode, the pump essentially acts as a liquid-ring pump. The rotating impeller generates a vacuum at the impeller’s ‘eye’ which draws air into the pump from the suction line. At the same time, it also creates a cylindrical ring of liquid on the inside of the pump casing. This effectively forms a gas-tight seal, stopping air returning from the discharge line to the suction line. Air bubbles are trapped in the liquid within the impeller’s vanes and transported to the discharge port. There, the air is expelled and the liquid returns under gravity to the reservoir (“Priming Chamber”) in the pump housing. Gradually, liquid rises up the suction line as the air is evacuated. This process continues until liquid replaces all the air in the suction piping and the pump. At this stage, the normal pumping mode commences, and liquid is discharged. If the attached discharge piping does not allow this separated air to escape out to the downstream discharge piping system, a bypass line may be required to evacuate it.
When the pump is shut off, the design of the priming chamber ensures that enough liquid is retained so that the pump can self prime on the next time it is operated. Liquid primed self priming pumps ability to operate in a mixture of air and liquid makes them far more versatile than their non self priming counterparts, which allows them to work in a broader range of environments and industries.
In Compressed Air Primed Self Priming Pumps, compressed air is blown through a jet into a tapered tube to create a vacuum, so air from the pump casing and suction line is drawn in with the compressed air and exhausted to the atmosphere. A non-return ball check valve seals out air from the discharge, allowing fluid to enter the pump body. Water then replaces the air which allows the pump to begin pumping. This pump type also avoids the potential build up of solids, since it has no priming chamber, so it can be used for sewage applications, plus it has dry running capability.
Vacuum Primed Self Priming Pumps typically has a vacuum pump and positive sealing float box installed at the pump discharge, close to the discharge valve. This allows it to pull a vacuum on the pump until it is full of water. Note that the maximum height that water can be lifted with a vacuum is 34 feet (at sea level), and that is with a perfect vacuum, and no liquid flowing. This pump type can have dry run capability, and is also capable of handling sewage.
Even a self priming pump has to be primed prior to its first operation. No matter the design, there is a priming chamber (integral or external) or some portion of the volute that will require filling prior to startup.
The discharge line must not be pressurized or blocked. The air in the suction side of the system being displaced by the liquid has to have somewhere to go, otherwise the pump will air bind.
The suction line must be air-tight. If air continues to be drawn into the pump, the pressure will never be reduced and fluid will not be drawn up the suction line.
Volume of the suction side piping to be minimized to reduce the priming time. With excessive priming times, there is a danger that the liquid charge will evaporate before the pump is primed.
When pumping liquid in cold conditions, the fluid in the priming chamber of the pump, usually water, will solidify if the ambient temperature drops below freezing for a sufficient period of time. When water freezes it expands and the casing will crack. Either drain the fluid out of the pump or supply a heat source when the ambient temperature is predicted to be below freezing.
Calculation of preliminary cooler capacity: Heat dissipation from hydraulic oil tanks, valves, pipes and hydraulic components is less than a few percent in standard mobile equipment and the cooler capacity must include some margins. Minimum cooler capacity, Ecooler = 0.25Ediesel
At least 25% of the input power must be dissipated by the cooler when peak power is utilized for long periods. In normal case however, the peak power is used for only short periods, thus the actual cooler capacity required might be considerably less. The oil volume in the hydraulic tank is also acting as a heat accumulator when peak power is used.
The system efficiency is very much dependent on the type of hydraulic work tool equipment, the hydraulic pumps and motors used and power input to the hydraulics may vary considerably. Each circuit must be evaluated and the load cycle estimated. New or modified systems must always be tested in practical work, covering all possible load cycles.
Things like restrictions and blockages can impede the flow of fluid to your pump. which could contribute to poor fluid flow. Air leak in suction line. Air present in the pump at startup. Insufficient supply of oil in pump. Clogged or dirty fluid filters. Clogged inlet lines or hoses. Blocked reservoir breather vent. Low oil in the reservoir
Now that we’ve ensured that the directional control is not reversed, it’s time to check that the drive motor itself is turning in the right direction. Sometimes incorrect installation leads to mismatched pipe routings between control valves and motors, which can reverse the direction of flow. Check to see that the motor is turning the pump in the right direction and if not - look at your piping.
Check to ensure that your pump drive motor is turning over and is developing the required speed and torque. In some cases, misalignment can cause binding of the drive shaft, which can prevent the motor from turning. If this is the case, correct the misalignment and inspect the motor for damage. If required, overhaul or replace motor.
Check to ensure the pump to motor coupling is undamaged. A sheared pump coupling is an obvious cause of failure, however the location of some pumps within hydraulic systems makes this difficult to check so it may go overlooked
It is possible that the entire flow could be passing over the relief valve, preventing the pressure from developing. Check that the relief valve is adjusted properly for the pump specifications and the application.
Seized bearings, or pump shafts and other internal damage may prevent the pump from operating all together. If everything else checks out, uncouple the pump and motor and check to see that the pump shaft is able to turn. If not, overhaul or replace the pump.
If your pump is having problems developing sufficient power, following this checklist will help you to pinpoint the problem. In some cases you may find a simple solution is the answer. If your pump is exhibiting any other issues such as noise problems, heat problems or flow problems, you may need to do some more investigation to address the root cause of your pump problem. To help, we’ve created a downloadable troubleshooting guide containing more information about each of these issues. So that you can keep your system up and running and avoid unplanned downtime. Download it here.
A gear pump is a type of positive displacement (PD) pump. It moves a fluid by repeatedly enclosing a fixed volume using interlocking cogs or gears, transferring it mechanically using a cyclic pumping action. It delivers a smooth pulse-free flow proportional to the rotational speed of its gears.
Gear pumps use the actions of rotating cogs or gears to transfer fluids. The rotating element develops a liquid seal with the pump casing and creates suction at the pump inlet. Fluid, drawn into the pump, is enclosed within the cavities of its rotating gears and transferred to the discharge. There are two basic designs of gear pump: external and internal(Figure 1).
An external gear pump consists of two identical, interlocking gears supported by separate shafts. Generally, one gear is driven by a motor and this drives the other gear (the idler). In some cases, both shafts may be driven by motors. The shafts are supported by bearings on each side of the casing.
As the gears come out of mesh on the inlet side of the pump, they create an expanded volume. Liquid flows into the cavities and is trapped by the gear teeth as the gears continue to rotate against the pump casing.
No fluid is transferred back through the centre, between the gears, because they are interlocked. Close tolerances between the gears and the casing allow the pump to develop suction at the inlet and prevent fluid from leaking back from the discharge side (although leakage is more likely with low viscosity liquids).
An internal gear pump operates on the same principle but the two interlocking gears are of different sizes with one rotating inside the other. The larger gear (the rotor) is an internal gear i.e. it has the teeth projecting on the inside. Within this is a smaller external gear (the idler –only the rotor is driven) mounted off-centre. This is designed to interlock with the rotor such that the gear teeth engage at one point. A pinion and bushing attached to the pump casing holds the idler in position. A fixed crescent-shaped partition or spacer fills the void created by the off-centre mounting position of the idler and acts as a seal between the inlet and outlet ports.
As the gears come out of mesh on the inlet side of the pump, they create an expanded volume. Liquid flows into the cavities and is trapped by the gear teeth as the gears continue to rotate against the pump casing and partition.
Gear pumps are compact and simple with a limited number of moving parts. They are unable to match the pressure generated by reciprocating pumps or the flow rates of centrifugal pumps but offer higher pressures and throughputs than vane or lobe pumps. Gear pumps are particularly suited for pumping oils and other high viscosity fluids.
Of the two designs, external gear pumps are capable of sustaining higher pressures (up to 3000 psi) and flow rates because of the more rigid shaft support and closer tolerances. Internal gear pumps have better suction capabilities and are suited to high viscosity fluids, although they have a useful operating range from 1cP to over 1,000,000cP. Since output is directly proportional to rotational speed, gear pumps are commonly used for metering and blending operations. Gear pumps can be engineered to handle aggressive liquids. While they are commonly made from cast iron or stainless steel, new alloys and composites allow the pumps to handle corrosive liquids such as sulphuric acid, sodium hypochlorite, ferric chloride and sodium hydroxide.
External gear pumps can also be used in hydraulic power applications, typically in vehicles, lifting machinery and mobile plant equipment. Driving a gear pump in reverse, using oil pumped from elsewhere in a system (normally by a tandem pump in the engine), creates a hydraulic motor. This is particularly useful to provide power in areas where electrical equipment is bulky, costly or inconvenient. Tractors, for example, rely on engine-driven external gear pumps to power their services.
Gear pumps are self-priming and can dry-lift although their priming characteristics improve if the gears are wetted. The gears need to be lubricated by the pumped fluid and should not be run dry for prolonged periods. Some gear pump designs can be run in either direction so the same pump can be used to load and unload a vessel, for example.
The close tolerances between the gears and casing mean that these types of pump are susceptible to wear particularly when used with abrasive fluids or feeds containing entrained solids. However, some designs of gear pumps, particularly internal variants, allow the handling of solids. External gear pumps have four bearings in the pumped medium, and tight tolerances, so are less suited to handling abrasive fluids. Internal gear pumps are more robust having only one bearing (sometimes two) running in the fluid. A gear pump should always have a strainer installed on the suction side to protect it from large, potentially damaging, solids.
Generally, if the pump is expected to handle abrasive solids it is advisable to select a pump with a higher capacity so it can be operated at lower speeds to reduce wear. However, it should be borne in mind that the volumetric efficiency of a gear pump is reduced at lower speeds and flow rates. A gear pump should not be operated too far from its recommended speed.
For high temperature applications, it is important to ensure that the operating temperature range is compatible with the pump specification. Thermal expansion of the casing and gears reduces clearances within a pump and this can also lead to increased wear, and in extreme cases, pump failure.
Despite the best precautions, gear pumps generally succumb to wear of the gears, casing and bearings over time. As clearances increase, there is a gradual reduction in efficiency and increase in flow slip: leakage of the pumped fluid from the discharge back to the suction side. Flow slip is proportional to the cube of the clearance between the cog teeth and casing so, in practice, wear has a small effect until a critical point is reached, from which performance degrades rapidly.
Gear pumps continue to pump against a back pressure and, if subjected to a downstream blockage will continue to pressurise the system until the pump, pipework or other equipment fails. Although most gear pumps are equipped with relief valves for this reason, it is always advisable to fit relief valves elsewhere in the system to protect downstream equipment.
Internal gear pumps, operating at low speed, are generally preferred for shear-sensitive liquids such as foodstuffs, paint and soaps. The higher speeds and lower clearances of external gear designs make them unsuitable for these applications. Internal gear pumps are also preferred when hygiene is important because of their mechanical simplicity and the fact that they are easy to strip down, clean and reassemble.
Gear pumps are commonly used for pumping high viscosity fluids such as oil, paints, resins or foodstuffs. They are preferred in any application where accurate dosing or high pressure output is required. The output of a gear pump is not greatly affected by pressure so they also tend to be preferred in any situation where the supply is irregular.
A gear pump moves a fluid by repeatedly enclosing a fixed volume within interlocking cogs or gears, transferring it mechanically to deliver a smooth pulse-free flow proportional to the rotational speed of its gears. There are two basic types: external and internal. An external gear pump consists of two identical, interlocking gears supported by separate shafts. An internal gear pump has two interlocking gears of different sizes with one rotating inside the other.
Gear pumps are commonly used for pumping high viscosity fluids such as oil, paints, resins or foodstuffs. They are also preferred in applications where accurate dosing or high pressure output is required. External gear pumps are capable of sustaining higher pressures (up to 7500 psi) whereas internal gear pumps have better suction capabilities and are more suited to high viscosity and shear-sensitive fluids.
Without hydraulics, modern construction equipment wouldn’t operate as effectively as it does. Because of this fluid-based system, heavy equipment can use small operator motions to create large movements in attachments and things they hold. Knowing when to repair the hydraulics of heavy equipment requires an understanding of the system. This guide provides important information you need to know about hydraulic systems used for heavy equipment.
The definition of a hydraulic system is an operation that uses pressurized fluid to power motion. The pressure of the fluid multiplies pressure put on it to increase the force at the output. A hydraulic system uses this fluid in cylinders or hydraulic power units to do work such as stop a vehicle through its brakes, lift a crane and its load or move a bucket on a loader.
Within a hydraulic system, there are components that put the incompressible fluid under pressure. Because the hydraulic oil does not press into a smaller space, the force applied to it gets transferred to the other end of the area where the oil is. The pressure exerted from the oil moves a large piston that can work alone or with additional cylinders to move things requiring extra force.
When equipping a device with a hydraulic system, you can increase the amount of work the system can do without increasing the effort you put into it. Applied to construction equipment, hydraulic power systems allow a small joystick movement to lift a tractor bucket filled with weighty rubble.
Such an operation would not be possible with humans using their muscles and shovels to lift the same amount of debris. For instance, a steam-driven predecessor of today’s hydraulic-powered construction equipment could move the same amount of substance in a day that two men equipped with a wheelbarrow could do in two weeks.
The improvements made to hydraulic systems have only increased their ability to make today’s equipment capable of the heavy lifting on construction sites that requires long-lasting reliability, power and control.
Power density: The output of hydraulics is many times greater than the force put into the system, reaching close to 7,000 pounds per square inch in some pieces of heavy construction equipment.
Hydraulic systems operate with one of two methods: cylinders or hydraulic power units. Cylinders are the original components used to multiply force with hydraulic fluid. However, advances in engineering now allow improved operations from larger hydraulic power units that increase the system’s work capability.
When using cylinders, hydraulic systems have a smaller and a larger cylinder. The smaller one has a piston for work put into the system. The piston presses down on hydraulic fluid in the small cylinder and flows into the bottom of the larger cylinder. The large cylinder also has a piston that moves based on the force of the oil.
The other type of system used is a hydraulic power unit that increases the capabilities of the system by using a pump and pressurized fluid to replace the small cylinder.
While the distance the small piston travels determines the output in a system that uses cylinders, those that have hydraulic power units do not have the limitation of physical distance. By raising the pressure of the fluid, the need for travel distance disappears, allowing for far higher output forces than with a cylinder system. This type of system is often used on construction equipment to achieve massive amounts of work and lifting capabilities.
The use of small and large cylinders and pistons works in some tiny devices, but the heavy loads and large movements required of construction equipment need more robust hydraulic solutions. For these more extensive devices, hydraulic power units replace cylinders for higher power output.
Because hydraulic power units (HPUs) bring in more fluid from a pump at higher pressures, they can create a force that equals a greater travel distance needed by a small piston. Since these HPUs do not have the physical size of a small cylinder to limit them, they can create far more force for the output than two-cylinder systems can.
An HPU contains all the components needed to operate the hydraulic system — including a pump, motor and fluid reservoir — in a self-contained area. The pump and its motor generate a small amount of pressure needed to move the system. When the hydraulic system starts, the pump delivers oil into the accumulator. Once the oil in the accumulator reaches the necessary pressure, the bigger piston moves, and a valve allows pressure to drop as the fluid returns to the reservoir.
Some hydraulic systems use two-stage pumps that permit faster pushing and pulling of a hydraulically operated force by shifting between high pressure and low flow rate and low pressure and high flow rate of the oil. A large reservoir is a requirement for many HPUs on earthmoving equipment. For some pieces of equipment that have multiple cylinders, the reservoirs can store dozens of gallons of fluid.
The hydraulic systems on construction equipment can operate various components. For example, the tracks on tracked backhoes have hydraulic drivers. Loaders often have a pair of pistons to move the bucket vertically, a couple to rotate the bucket to turn out contents and a set to open the bucket’s sides. Dump trucks have a comparatively simple operation, only requiring one or two cylinders to lift the bed.
Cranes also use hydraulics in many ways. For cranes that have outriggers to lift the entire system, hydraulic systems provide the power to hoist the multi-ton vehicle vertically. To turn the crane’s load on a boom, a hydraulic system moves the Rotex gear. The boom also telescopes in or out thanks to the motions of hydraulics. The operator’s controls connect to the hydraulic hoses in a crane and other similarly operated construction equipment.
Using the controls in the operator’s cab changes the flow of hydraulic fluid in the system, allowing for parts of the equipment to move. The fluid routing happens at the spool valves, which link oil lines to the pump and each other. These valves change the direction of the fluid, which moves the hydraulic force to the parts of the equipment where the operator needs it to go.
Because the hydraulic systems in heavy equipment allow these pieces to perform vital work, problems with the hydraulic power unit’s motor, pump or reservoir can hamper productivity on a job site. In these situations, it’s helpful to identify the symptoms of the problem and get the equipment to a service shop for repairs to minimize downtime.
While reliable, the hydraulic system for earthmoving equipment and other similar vehicles can have problems. Major symptoms of hydraulic system issues include the following:
Noisy operation means there’s excessive noise coming from some part of the equipment. Listen carefully for the source of the sound because this can help a certified technician identify potential problems. For instance, a noisy pump could indicate air in the hydraulic fluid, a worn pump or misaligned couplings.
Noise coming from the pump’s motor could also be a sign of misaligned couplings or wear in the pump’s engine. When you hear extra noise coming from the relief valve, the valve may not have the correct setting or a poppet on it may have worn.
Be cautious about making a diagnosis of your hydraulic system only from the sounds and their locations. A certified technician has the tools and tests to determine the exact cause of the noise and provide a repair for it.
Problems with hydraulic fluid flow fall into three categories – too much flow, not enough flow or no current flow. Because these groupings cover a wide range of causes, a certified technician may need to conduct additional diagnostic tests or look for other factors to find the exact cause.
Many of these problems will require service to the pump or replacement parts in the hydraulic pump. The certified technician may also need to make repairs or part replacements based on the wear sustained by your equipment’s hydraulic system.
Abnormal movement of a hydraulic system can lead to dangerous situations on a construction site. Hydraulically operated components must move as expected. Erratic, slow, inconsistent or limited movement all indicate serious problems that need immediate repairs. These faulty movements may happen in conjunction with other issues, such as oil flow problems or noisy operation. For example, a lack of hydraulic fluid flowing through the pump may completely restrict movement. Any air in the oil may cause both noisy use and erratic operation.
Incorrect pressure in a hydraulic system closely mirrors faulty operation. If your equipment shows faulty operation, a technician may need to look at the pressure of the fluid and determine the cause of the pressure problem first. For instance, air in the oil may cause both erratic pressure and erratic operation of the hydraulic mechanism. Low pressure could happen from a damaged pump or pressure reduction valve and cause the system to operate slowly.
A hydraulic system may overheat when the fluid overheats. Whichever component of the system runs hot can provide a clue to the source of the excess heat. For instance, if the pump or motor run hot, the system may have too high of a load put on it, the engine may have damage or the relief valve may be set too high.
As with other hydraulic system problems, an expert must conduct a thorough investigation of the entire system to identify the sources of any issues. When looking for an expert, choose a certified technician who has the replacement parts for your equipment’s brand on hand. This combination ensures your heavy equipment will be repaired correctly and as quickly as possible.
If your hydraulic system needs service or replacement parts, connect with us at Prime Source. Our shop service capabilities range from offering replacement parts for all makes of heavy equipment to providing repairs for hydraulic systems. Our certified technicians can inspect your equipment’s hydraulic system as a whole and make any necessary repairs or part replacements.
A hydraulic pump converts mechanical energy into fluid power. It"s used in hydraulic systems to perform work, such as lifting heavy loads in excavators or jacks to being used in hydraulic splitters. This article focuses on how hydraulic pumps operate, different types of hydraulic pumps, and their applications.
A hydraulic pump operates on positive displacement, where a confined fluid is subjected to pressure using a reciprocating or rotary action. The pump"s driving force is supplied by a prime mover, such as an electric motor, internal combustion engine, human labor (Figure 1), or compressed air (Figure 2), which drives the impeller, gear (Figure 3), or vane to create a flow of fluid within the pump"s housing.
A hydraulic pump’s mechanical action creates a vacuum at the pump’s inlet, which allows atmospheric pressure to force fluid into the pump. The drawn in fluid creates a vacuum at the inlet chamber, which allows the fluid to then be forced towards the outlet at a high pressure.
Vane pump:Vanes are pushed outwards by centrifugal force and pushed back into the rotor as they move past the pump inlet and outlet, generating fluid flow and pressure.
Piston pump:A piston is moved back and forth within a cylinder, creating chambers of varying size that draw in and compress fluid, generating fluid flow and pressure.
A hydraulic pump"s performance is determined by the size and shape of the pump"s internal chambers, the speed at which the pump operates, and the power supplied to the pump. Hydraulic pumps use an incompressible fluid, usually petroleum oil or a food-safe alternative, as the working fluid. The fluid must have lubrication properties and be able to operate at high temperatures. The type of fluid used may depend on safety requirements, such as fire resistance or food preparation.
Air hydraulic pump:These pumps have a compact design and do not require an external power source. However, a reliable source of compressed air is necessary and is limited by the supply pressure of compressed air.
Electric hydraulic pump:They have a reliable and efficient power source and can be easily integrated into existing systems. However, these pumps require a constant power source, may be affected by power outages, and require additional electrical safety measures. Also, they have a higher upfront cost than other pump types.
Gas-powered hydraulic pump:Gas-powered pumps are portable hydraulic pumps which are easy to use in outdoor and remote environments. However, they are limited by fuel supply, have higher emissions compared to other hydraulic pumps, and the fuel systems require regular maintenance.
Manual hydraulic pump:They are easy to transport and do not require a power source. However, they are limited by the operator’s physical ability, have a lower flow rate than other hydraulic pump types, and may require extra time to complete tasks.
Hydraulic hand pump:Hydraulic hand pumps are suitable for small-scale, and low-pressure applications and typically cost less than hydraulic foot pumps.
Hydraulic foot pump:Hydraulic foot pumps are suitable for heavy-duty and high-pressure applications and require less effort than hydraulic hand pumps.
Hydraulic pumps can be single-acting or double-acting. Single-acting pumps have a single port that hydraulic fluid enters to extend the pump’s cylinder. Double-acting pumps have two ports, one for extending the cylinder and one for retracting the cylinder.
Single-acting:With single-acting hydraulic pumps, the cylinder extends when hydraulic fluid enters it. The cylinder will retract with a spring, with gravity, or from the load.
Double-acting:With double-acting hydraulic pumps, the cylinder retracts when hydraulic fluid enters the top port. The cylinder goes back to its starting position.
Single-acting:Single-acting hydraulic pumps are suitable for simple applications that only need linear movement in one direction. For example, such as lifting an object or pressing a load.
Double-acting:Double-acting hydraulic pumps are for applications that need precise linear movement in two directions, such as elevators and forklifts.
Pressure:Hydraulic gear pumps and hydraulic vane pumps are suitable for low-pressure applications, and hydraulic piston pumps are suitable for high-pressure applications.
Cost:Gear pumps are the least expensive to purchase and maintain, whereas piston pumps are the most expensive. Vane pumps land somewhere between the other two in cost.
Efficiency:Gear pumps are the least efficient. They typically have 80% efficiency, meaning 10 mechanical horsepower turns into 8 hydraulic horsepower. Vane pumps are more efficient than gear pumps, and piston pumps are the most efficient with up to 95% efficiency.
Automotive industry:In the automotive industry, hydraulic pumps are combined with jacks and engine hoists for lifting vehicles, platforms, heavy loads, and pulling engines.
Process and manufacturing:Heavy-duty hydraulic pumps are used for driving and tapping applications, turning heavy valves, tightening, and expanding applications.
Despite the different pump mechanism types in hydraulic pumps, they are categorized based on size (pressure output) and driving force (manual, air, electric, and fuel-powered). There are several parameters to consider while selecting the right hydraulic pump for an application. The most important parameters are described below:
Source of driving force: Is it to be manually operated (by hand or foot), air from a compressor, electrical power, or a fuel engine as a prime mover? Other factors that may affect the driving force type are whether it will be remotely operated or not, speed of operation, and load requirement.
Speed of operation: If it is a manual hydraulic pump, should it be a single-speed or double-speed? How much volume of fluid per handle stroke? When using a powered hydraulic pump, how much volume per minute? Air, gas, and electric-powered hydraulic pumps are useful for high-volume flows.
Portability: Manual hand hydraulic pumps are usually portable but with lower output, while fuel power has high-output pressure but stationary for remote operations in places without electricity. Electric hydraulic pumps can be both mobile and stationary, as well as air hydraulic pumps. Air hydraulic pumps require compressed air at the operation site.
Operating temperature: The application operating temperature can affect the size of the oil reservoir needed, the type of fluid, and the materials used for the pump components. The oil is the operating fluid but also serves as a cooling liquid in heavy-duty hydraulic pumps.
Operating noise: Consider if the environment has a noise requirement. A hydraulic pump with a fuel engine will generate a higher noise than an electric hydraulic pump of the same size.
Spark-free: Should the hydraulic pump be spark-free due to a possible explosive environment? Remember, most operating fluids are derivatives of petroleum oil, but there are spark-free options.
A hydraulic pump transforms mechanical energy into fluid energy. A relatively low amount of input power can turn into a large amount of output power for lifting heavy loads.
A hydraulic pump works by using mechanical energy to pressurize fluid in a closed system. This pressurized fluid is then used to drive machinery such as excavators, presses, and lifts.
A hydraulic ram pump leverages the energy of falling water to move water to a higher height without the usage of external power. It is made up of a valve, a pressure chamber, and inlet and exit pipes.
A water pump moves water from one area to another, whereas a hydraulic pump"s purpose is to overcome a pressure that is dependent on a load, like a heavy car.
Most experts agree that the majority of centrifugal pump problems occur on the suction side of the pump. Based solely on my experience, I would state the percentage is at least 80 percent, and in the case of self-priming pumps I am sure the percentage is higher.
Even a self-priming pump has to be primed prior to the first operation. No matter the manufacturer, there is a priming chamber (integral or external) or some portion of the volute that will require filling prior to startup. Please read the manual and/or contact the manufacturer for details. There are other methods to prime a pump, which include ancillary pumps, vacuum, vacuum ejectors and/or eductors. This article only addresses liquid self-priming centrifugal pumps.
Sometimes the pump will require manual re-priming after the initial prime. There can be several reasons for re-priming, one of the most common is evaporation of the fluid, and other reasons include leakage, pump movement and other maintenance related matters.
At sea level in a perfect world, you can theoretically lift 65-degree water 34 feet with a self-primer. I normally caution users to limit their suction lift to a maximum of 25 feet due to factors such as fluid temperature (think vapor pressure), specific gravity, friction, system leakage, pump inefficiencies and elevation above sea level.
Place the pump as close as possible to the suction source. Usually 25 to 30 feet is the maximum recommended distance. Prudent system design dictates that the suction pipe length be held to a minimum to promote long pump life. Every section of suction piping equates to a volume of air that must be removed when the pump starts. Best practices say to reduce priming time to a minimum.
Some system designers will add foot valves to mitigate the prime time and strainers to preclude the introduction of solids into the pump. A foot valve is in essence a check valve placed at the beginning (bottom) of the suction line. My experience is that foot valves add undesired friction and will leak or fail closed (or partially closed) at some point. I typically do not recommend foot valves for use on commercial and industrial self-primer applications. For similar reasons I do not recommend suction strainers. If the pump cannot handle solids and a strainer is utilized, monitor the differential pressure across the strainer. Most industrial self-priming pumps are of robust design and can handle passing solids, but check with the manufacturer. Note: A few applications may perform better with a foot valve.
I frequently need to point out to end users that the suction line on a self-primer pump in operation is at less than atmospheric pressure and so there will not be a leak of the liquid out of the suction line. There can, however, be a leak of air into the line. It is possible to have a suction line at 20 inches of Hg (vacuum) when the pump is operating. As a tip for field problem solving, I frequently use plastic wrap around the flanges or suspected areas to test for ingress leaks.
Simply as a general guideline, if your pump takes more than four minutes to prime than you should shut the pump down and look for and correct the cause of the problem.
The air in the suction side of the system being displaced by the liquid has to have somewhere to go, otherwise the pump will air bind. Centrifugal pumps are not compressors. Water is approximately 840 times denser than air. As an example if a pump was rated at a discharge pressure of 210 psig pumping water, the pump could theoretically compress air to approximately one quarter of a pound (0.25 psig) (210 psig divided by 840 is equal to 0.25). If the pump discharge valve and/or the discharge check valve are shut, the generated pressure of 0.25 psig will not be able to overcome the valves.
Within the confines of the article I will simply state that the air must be vented to an area of lower pressure for the pump to properly prime. There are many acceptable methods to accomplish the process, please contact your pump manufacturer or the author.
Most experienced pump users know that as a general rule you should always design the suction line to be one size larger than the pump suction. Self–priming pumps are an exception, and the suction piping should be the same size as the pump suction. The infraction of the rules is encouraged because of the added air volume that bigger suction lines require. More air means more priming time.
The suction pipe should rise continuously to the pump and not higher. In the field, I frequently see suction pipes with high points before the pump suction usually due to obstructions. These high points become a place for the air and other non-condensable gases to collect and will bind the pump suction line. Never install piping that is smaller than the pump suction in any pump.
I covered net positive suction head available (NPSHA) in last month"s article. I strongly recommend calculating the NPSHA for self-primers, as it is a great method to identify potential problem areas. For example, if the fluid is 160 degrees F, the vapor pressure of the fluid alone will likely preclude you from this application. For example, water at 160 F has a vapor pressure that equates to a negative 11 feet.
The sump you are drawing from will likely have operating levels that are constantly changing. At some value of minimum submergence it will be possible for the system to create a vortex and air bind the pump. I covered submergence in the last article, but simply defined, it is the minimum distance from the top of the fluid to the center of the suction line that will prevent a vortex from initiation. Even if you do not completely air bind, the pump performance can be affected.
This problem occurs more often in areas that have infrequent freezing weather, but can happen anywhere the temperature will drop below freezing for an hour or more. The fluid in the priming chamber of the pump, usually water, will solidify if the ambient temperature drops below freezing for a sufficient period of time. When water freezes it expands and the casing will crack. The casing will require replacement at a high cost. Either drain the fluid out of the pump or supply a heat source when the ambient temperature is predicted to be below freezing.
Unlike an ANSI pump, the impeller will stay in place on most self-primers for a period of time (unless it is an ANSI self-primer. Eventually the impeller may come loose and damage the pump. The backward-running impeller generally will create about 50 percent of the rated flow and, depending on the impeller specific speed (NS), will generate about 50 percent of the rated head. Reduced efficiency of the wrong rotation will likely prevent it from priming or operating correctly but in the simplest of suction lift cases.
The pump performance must be de-rated for higher elevation changes (less absolute pressure less NPSHa). If the pump is engine driven in lieu of an electric motor, the resulting intermittent torque introduces limitations to the shaft design capabilities.
Check that the pump shaft is rotating. Even though coupling guards and C-face mounts can make this difficult to confirm, it is important to establish if your pump shaft is rotating. If it isn’t, this could be an indication of a more severe issue, and this should be investigated immediately.
Check the oil level. This one tends to be the more obvious check, as it is often one of the only factors inspected before the pump is changed. The oil level should be three inches above the pump suction. Otherwise, a vortex can form in the reservoir, allowing air into the pump.
What does the pump sound like when it is operating normally? Vane pumps generally are quieter than piston and gear pumps. If the pump has a high-pitched whining sound, it most likely is cavitating. If it has a knocking sound, like marbles rattling around, then aeration is the likely cause.
Cavitation is the formation and collapse of air cavities in the liquid. When the pump cannot get the total volume of oil it needs, cavitation occurs. Hydraulic oil contains approximately nine percent dissolved air. When the pump does not receive adequate oil volume at its suction port, high vacuum pressure occurs.
This dissolved air is pulled out of the oil on the suction side and then collapses or implodes on the pressure side. The implosions produce a very steady, high-pitched sound. As the air bubbles collapse, the inside of the pump is damaged.
While cavitation is a devastating development, with proper preventative maintenance practices and a quality monitoring system, early detection and deterrence remain attainable goals. UE System’s UltraTrak 850S CD pump cavitation sensor is a Smart Analog Sensor designed and optimized to detect cavitation on pumps earlier by measuring the ultrasound produced as cavitation starts to develop early-onset bubbles in the pump. By continuously monitoring the impact caused by cavitation, the system provides a simple, single value to trend and alert when cavitation is occurring.
The oil viscosity is too high. Low oil temperature increases the oil viscosity, making it harder for the oil to reach the pump. Most hydraulic systems should not be started with the oil any colder than 40°F and should not be put under load until the oil is at least 70°F.
Many reservoirs do not have heaters, particularly in the South. Even when heaters are available, they are often disconnected. While the damage may not be immediate, if a pump is continually started up when the oil is too cold, the pump will fail prematurely.
The suction filter or strainer is contaminated. A strainer is typically 74 or 149 microns in size and is used to keep “large” particles out of the pump. The strainer may be located inside or outside the reservoir. Strainers located inside the reservoir are out of sight and out of mind. Many times, maintenance personnel are not even aware that there is a strainer in the reservoir.
The suction strainer should be removed from the line or reservoir and cleaned a minimum of once a year. Years ago, a plant sought out help to troubleshoot a system that had already had five pumps changed within a single week. Upon closer inspection, it was discovered that the breather cap was missing, allowing dirty air to flow directly into the reservoir.
A check of the hydraulic schematic showed a strainer in the suction line inside the tank. When the strainer was removed, a shop rag was found wrapped around the screen mesh. Apparently, someone had used the rag to plug the breather cap opening, and it had then fallen into the tank. Contamination can come from a variety of different sources, so it pays to be vigilant and responsible with our practices and reliability measures.
The electric motor is driving the hydraulic pump at a speed that is higher than the pump’s rating. All pumps have a recommended maximum drive speed. If the speed is too high, a higher volume of oil will be needed at the suction port.
Due to the size of the suction port, adequate oil cannot fill the suction cavity in the pump, resulting in cavitation. Although this rarely happens, some pumps are rated at a maximum drive speed of 1,200 revolutions per minute (RPM), while others have a maximum speed of 3,600 RPM. The drive speed should be checked any time a pump is replaced with a different brand or model.
Every one of these devastating causes of cavitation threatens to cause major, irreversible damage to your equipment. Therefore, it’s not only critical to have proper, proactive practices in place, but also a monitoring system that can continuously protect your valuable assets, such as UE System’s UltraTrak 850S CD pump cavitation senor. These sensors regularly monitor the health of your pumps and alert you immediately if cavitation symptoms are present, allowing you to take corrective action before it’s too late.
Aeration is sometimes known as pseudo cavitation because air is entering the pump suction cavity. However, the causes of aeration are entirely different than that of cavitation. While cavitation pulls air out of the oil, aeration is the result of outside air entering the pump’s suction line.
Several factors can cause aeration, including an air leak in the suction line. This could be in the form of a loose connection, a cracked line, or an improper fitting seal. One method of finding the leak is to squirt oil around the suction line fittings. The fluid will be momentarily drawn into the suction line, and the knocking sound inside the pump will stop for a short period of time once the airflow path is found.
A bad shaft seal can also cause aeration if the system is supplied by one or more fixed displacement pumps. Oil that bypasses inside a fixed displacement pump is ported back to the suction port. If the shaft seal is worn or damaged, air can flow through the seal and into the pump’s suction cavity.
As mentioned previously, if the oil level is too low, oil can enter the suction line and flow into the pump. Therefore, always check the oil level with all cylinders in the retracted position.
If a new pump is installed and pressure will not build, the shaft may be rotating in the wrong direction. Some gear pumps can be rotated in either direction, but most have an arrow on the housing indicating the direction of rotation, as depicted in Figure 2.
Pump rotation should always be viewed from the shaft end. If the pump is rotated in the wrong direction, adequate fluid will not fill the suction port due to the pump’s internal design.
A fixed displacement pump delivers a constant volume of oil for a given shaft speed. A relief valve must be included downstream of the pump to limit the maximum pressure in the system.
After the visual and sound checks are made, the next step is to determine whether you have a volume or pressure problem. If the pressure will not build to the desired level, isolate the pump and relief valve from the system. This can be done by closing a valve, plugging the line downstream, or blocking the relief valve. If the pressure builds when this is done, there is a component downstream of the isolation point that is bypassing. If the pressure does not build up, the pump or relief valve is bad.
If the system is operating at a slower speed, a volume problem exists. Pumps wear over time, which results in less oil being delivered. While a flow meter can be installed in the pump’s outlet line, this is not always practical, as the proper fittings and adapters may not be available. To determine if the pump is badly worn and bypassing, first check the current to the electric motor. If possible, this test should be made when the pump is new to establish a reference. Electric motor horsepower is relative to the hydraulic horsepower required by the system.
For example, if a 50-GPM pump is used and the maximum pressure is 1,500 psi, a 50-hp motor will be required. If the pump is delivering less oil than when it was new, the current to drive the pump will drop. A 230-volt, 50-hp motor has an average full load rating of 130 amps. If the amperage is considerably lower, the pump is most likely bypassing and should be changed.
Figure 4.To isolate a fixed displacement pump and relief valve from the system, close a valve or plug the line downstream (left). If pressure builds, a component downstream of the isolation point is bypassing (right).
The most common type of variable displacement pump is the pressure-compensating design. The compensator setting limits the maximum pressure at the pump’s outlet port. The pump should be isolated as described for the fixed displacement pump.
If pressure does not build up, the relief valve or pump compensator may be bad. Prior to checking either component, perform the necessary lockout procedures and verify that the pressure at the outlet port is zero psi. The relief valve and compensator can then be taken apart and checked for contamination, wear, and broken springs.
Install a flow meter in the case drain line and check the flow rate. Most variable displacement pumps bypass one to three percent of the maximum pump volume through the case drain line. If the flow rate reaches 10 percent, the pump should be changed. Permanently installing a flow meter in the case drain line is an excellent reliability and troubleshooting tool.
Ensure the compensator is 200 psi above the maximum load pressure. If set too low, the compensator spool will shift and start reducing the pump volume when the system is calling for maximum volume.
Performing these recommended tests should help you make good decisions about the condition of your pumps or the cause of pump failures. If you change a pump, have a reason for changing it. Don’t just do it because you have a spare one in stock.
Conduct a reliability assessment on each of your hydraulic systems so when an issue occurs, you will have current pressure and temperature readings to consult.
Al Smiley is the president of GPM Hydraulic Consulting Inc., located in Monroe, Georgia. Since 1994, GPM has provided hydraulic training, consulting and reliability assessments to companies in t...
In waterworks and wastewater systems, pumps are commonly installed at the source to raise the water level and at intermediate points to boost the water pressure. The components and design of a pumping station are vital to its effectiveness. Centrifugal pumps are most often used in water and wastewater systems, making it important to learn how they work and how to design them. Centrifugal pumps have several advantages over other types of pumps, including:
A centrifugal pump consists of a rotating shaft that is connected to an impeller, which is usually comprised of curved blades. The impeller rotates within its casing and sucks the fluid through the eye of the casing (point 1 in Figure 10.1). The fluid’s kinetic energy increases due to the energy added by the impeller and enters the discharge end of the casing that has an expanding area (point 2 in Figure 10.1). The pressure within the fluid increases accordingly.
The characteristic curves of commercial pumps are provided by manufacturers. Otherwise, a pump should be tested in the laboratory, under various discharge and head conditions, to produce such curves. If a single pump is incapable of delivering the design flow rate and pressure, additional pumps, in series or parallel with the original pump, can be considered. The characteristic curves of pumps in series or parallel should be constructed since this information helps engineers select the types of pumps needed and how they should be configured.
Many pumps are in use around the world to handle liquids, gases, or liquid-solid mixtures. There are pumps in cars, swimming pools, boats, water treatment facilities, water wells, etc. Centrifugal pumps are commonly used in water, sewage, petroleum, and petrochemical pumping. It is important to select the pump that will best serve the project’s needs.
The objective of this experiment is to determine the operational characteristics of two centrifugal pumps when they are configured as a single pump, two pumps in series, and two pumps in parallel.
Each configuration