Pump Failure

There are several reasons for pump failure and most are generally connected with improper usage. System abuse may be the direct or indirect cause of pump problems.

Damage to pumps can occur due to insufficient water supply or a sudden increase in water temperature, both of which can cause cavitations. Additionally, over-revving the engine, which some operators try as a way to improve pump performance with more viscous liquids or with inadequate water supplies, can damage the pump. Over-revving is most likely to occur with cold water, gasoline engine-powered cleaners.

Pump damage, including thrown or broken connecting rods, may result from inadequate or improper lubrication but are more likely to be the result of operation of the pump at higher than rated rpm and pressure.

Pump Service – Why It Probably Isn’t Needed
The high-pressure pump is generally one of the most durable and best-constructed components in a high pressure cleaner. Consequently, pump operation is amazingly trouble-free. However, the well-engineered pump may be installed in a not-so-well-engineered high pressure cleaning system.

Suspected pump problems are often not what they seem. In almost 99 percent of all cases, system problems, which might be initially diagnosed as pump problems, are actually problems elsewhere in the system. Low pressure, chattering and a number of other pump maladies are more often symptoms of problems outside, rather than inside the pump. The high pressure pump, if properly installed and operated, will function for thousands of hours unless it is of defective manufacture.

All pumps have wearable parts, which eventually will need to be replaced. This replacement is called "rebuilding" the pump and generally includes the inspection, cleaning and lubrication of moving parts that are not replaced during the process. Absence of debris in the water supply and the avoidance of cavitation will extend the period of the pump operation before rebuilding is necessary.

Some pump designs, of course, are less prone to failure than others. But as any design develops, the manufacturer eventually works out problems. In most cases, the high pressure pump is likely to outlast most other high pressure cleaning system components so long as the pump is properly installed and the system properly operated.

Kinds of Wearable Parts

Wearable pump parts include check valve seats, check valve plates, check valve springs, o-rings, v-packing and oil seals. The normal action of the pump will cause gradual even wear of such parts as the valve plate and seat and packing and seals. For example: metal-to-metal contact between the valve seat and plate will eventually result in discernable wear after normal operation. Cavitation, debris-contaminated water, harsh chemicals or other abnormal operating conditions can accelerate wear on internal pump parts.

Wearable parts along with characteristic wear patterns are listed below.

Check valve assemblies. Wear will result from metal to metal contact over a period of time. Such wear will generally appear as an even, circular scoring on both components at the point where the valve seat and plate meet. Eventually this wear will cause valve failure. Uneven wear patterns on the check valve seat and plate can be indicative of additional problems. Debris caught between the valve plate and seat can cause localized scoring of the metal.

Use of harsh or corrosive chemicals can actually eat away metal valve parts to the point where they are no longer functional. If an acid is used with a pump with aluminum valve parts, such wear will occur very rapidly. Normal pump use will eventually weaken the valve springs.

V-packings. V-packings or high-pressure water seals are in constant contact with the moving plunger surface and wear will result from this friction and associated load stress on the packing material during normal pump operation. Heat resulting from this surface contact as well as from crankcase friction retained in the closed loop bypass system can also contribute to packing wear.

Some chemicals are antagonistic to various packing materials. Of materials used in packings and seals, Teflon is the most chemical resistant overall; Viton, offered as an option on many pump types, is quite resistant to the action of acids commonly used in high pressure cleaning but is not so tolerant of caustics used in such applications; Nitrile, commonly used in a variety of packing, seals and o-ring, will tolerate intermittent use with acids and is quite resistant to the action of caustics; and EPDM, used in high temperature applications, has good acid resistance and excellent resistance to caustics, but poor resistance to petroleum-based fluids.

Oil seals. These seals are subject to friction wearing similar to that experienced by v-packing but are not normally exposed to chemicals. However, dirt and debris may enter the seal area and cause accelerated wear. Low oil levels or dirty oil can cause abnormally rapid oil seal wear.

O-rings. Although generally not subject to wear from friction, chemicals, water and heat cause the o-rings to dry up and crack. This is more an aging than a wear process.

Chemicals Can Dictate Pump Materials
The type of cleaning chemicals to be used can indicate the need for a certain type of pump material. A pump with aluminum components should never be used with a very acidic chemical such as aluminum brightener (hydrofluoric acid). The aluminum components literally dissolve in the acid.

The pump should be thoroughly flushed with fresh water after any cleaning chemical passes through the pump (upstream chemical injection). To flush the system of chemicals, shut off the chemical valve and operate without chemical until nothing but clear water comes out of the machine. To preserve other components, such as the chemical valve, you may insert the chemical supply hose into a bucket of clean water and open the chemical valve completely, flushing the chemical valve and lines. Many types of cleaning chemicals can also cause scale in the pump, which can degrade pump performance.

Note: Heavy scale in the pump is generally from cleaning chemical deposits. Minerals suspended in hard water generally do not precipitate out until the water is heated and hard water scale is consequently most common in the coil and beyond.

Pump Failure As A Result Of Installation Or Operation
In nearly all instances, pump failure is the result of improper pump installation or operation rather than normal wear. Common causes of destructive failure are installation of a direct drive pump unit with the wrong motor or engine (generally inadequate shaft clearance), installation of a pump so that it operates at a much higher speed than it is designed for, operation of a pump with an inadequate water supply or with a water supply that is too hot (cavitation), allowing the pump to freeze up in winter, or operation of a pump with incompatible chemicals or debris in the water supply.

Pump failure can also occur as a result of continued operation with very hard water or scale-producing cleaning chemicals, which will eventually cause scale buildup. One of the most common causes of pump failure is improper or unnecessary service. Often this is the result of an operator attempting pump service. However, a competitor’s service department may be responsible for improper pump service as well. In many instances a relatively sophisticated customer will ask that his cleaning system’s pump be rebuilt. In a large percentage of these cases, rebuilding the pump is unnecessary.

Does It Really Need Rebuilding?

Improperly rebuilding a pump is more likely to cause pump failure than even most types of improper operation. This is somewhat puzzling, because rebuilding a pump is a relatively straightforward process. Most commonly, rebuilding a pump will require work only on the wet side of the pump.

Rebuilding the wet side of a pump consists of these steps, although not necessarily in this order. (Some pump designs require removal of the manifold for access to some or all of the check valve assemblies.)

1.) Accessing check valves and cleaning or replacement of valve assemblies as necessary. This may be as simple as removing valve plugs or may require manifold removal for access to some or all of the check valves.
2.) Removal of the manifold. The manifold may be a one-or two-part assembly.
3.) Inspection and cleaning or replacement of plungers. In wobble-or swash-plate pumps this will require entry into the crankcase.
4.) Inspection and cleaning or replacement of v-packing assemblies or stuffing boxes.
5.) Reassembly of the pump.

Important Note: Whenever a pump is dismantled, carefully clean each part before replacing. Make certain no debris from this cleaning process finds its way into the reassembled pump.

In many cases, when a pump is rebuilt, wearable items showing moderate wear may be replaced if similar wearable components in other cylinders show enough wear that replacement is required. A pump rebuild should be forever, or as close to it as possible. Each time the pump is serviced, the chance of pump failure as a result of improper service increases. The operator should be left with no reason or desire to open the pump for service. For maximum rebuild life, all parts should be clean, lubricated as necessary and fit properly in the pump.

Fools Rush In
The first rule for rebuilding pumps is to not do so unless it is necessary. In fact, even removing the pump head or manifolds may not be necessary in many cases that might initially be diagnosed as pump problems. Take care to make certain that other possible causes of the problem being diagnosed have been checked before pulling the manifold off of the pump.

Note: If the pumps check valves may be accessed from the outside, inspecting check valves for sticking is simple and does not require the time and effort necessary for removal of the pump manifold or manifolds.

Make sure the pump really needs rebuilding. Valve wear and condition may be indications of the need for pump rebuilding. Heavy wear would indicate a greater need for rebuilding than would light valve wear.

How Pumps Differ
Pumps are divided into categories according to certain characteristics. These include:
1. Whether a plunger or piston moves through the cylinder.
2. Whether the plungers are ceramic or stainless steel.
3. How many cylinders the pump has. Two-cylinder pumps are called duplex pumps; three cylinder, triplex; four-cylinder, quadraplex; and five-cylinder, quintuplex.
4. Whether the manifold is one – or two-piece.
5. Whether check valves can be accessed without removal of the manifold.
6. Whether a crankshaft or some other method, such as a wobble plate or cam bearing, is used to drive the plungers or pistons.
7. The method of crankcase lubrication such as oil bath immersed or grease fitting.
8. Whether the recommended rpm allows direct drive or requires a belt or gearbox.
9. Whether the pump shaft is solid or hollow.

The majority of pumps used in the high pressure cleaning industry are either duplex or triplex ceramic plunger, crankshaft-driven, oil-bath pumps. Most of the ceramic plunger pumps used in new equipment have one-piece manifolds and allow access to valve assemblies without removal of the manifold. In addition to these differences, pumps may be divided into other subcategories according to design.

Ceramic Plunger Pumps
Ceramic plunger pumps have a hardened ceramic plunger, which moves back and forth in the cylinder. This plunger is impregnated with metal for added hardness. The plunger is simply a ceramic tube open at both ends. It is mounted on the connecting rod with a plunger bolt, which closes the manifold or wet end of the plunger. The plunger moves through a fixed packing and oil seal.

Piston Cup Pumps

Although they may be similar in external appearance, piston pumps differ from plunger pumps in internal operation in a couple of basic ways. The piston pump sucks water into the cylinder at the same time that it pushes the water out. This works because the piston also serves as a mechanically actuated check valve. It is closed on the compression stroke and open on the return stroke to allow the piston to pass back through the water that has already been drawn into the cylinder behind the piston.

The packing arrangements on piston and plunger pumps differ as well. The packing on a piston pump is fixed loosely in place and the packing moves through the cylinder. This arrangement is called a floating seal or floating packing.

Pump Type And Service
Two particular design distinctions, which are important in determining how the pump is disassembled and rebuilt, are the ease of access of check valves (whether the manifold or pump head must be removed to inspect the valves) and the type of manifold (whether it is one-piece or two-piece).

Procedures for inspecting valves and packing vary according to which of these two-sub classifications fit the pump design. Pumps with easily accessible valves will have visible valve plugs on the manifold. These generally can be removed with a standard-size socket. Common sizes are 22mm and 30mm.

Some pumps with one-piece manifolds may have one set valves accessible from the outside of the manifold and another set , which requires manifold removal for access. And some pumps with one-piece manifolds may require manifold removal for valve access. Pumps with one-piece manifolds are usually plunger pumps. Generally, split manifold pumps will require removal of at least one manifold component for valve access. These pumps are usually piston cup pumps. Some early plunger pumps were made with split manifolds; however, pumps of this type were not produced in high numbers.

Check Valves
The check valves are one-way doors, which direct water flow through the cylinders. The outlet check valve allows water flow out of the pump but not back in. The inlet check valve allows water flow into the pump but not back out. A spring is usually used to keep the check valve seated. This spring also helps return the valve to its seat quickly. A retainer, often made of plastic, keeps the spring in place. The valve action, however, is dependent on the flow of water, not the
spring. The valve will only open in one direction. Water flow from the other direction presses the valve onto its seat.