Worn nozzle(s) are the most frequent cause of low pressure. Never adjust the pressure regulating valve to compensate for worn nozzles. This will result in over-pressurization and possible damage to the pump. Replace nozzle(s) with the proper size when pressure drops or on a regular maintenance schedule. Remember to factor in approximately 5-10% by-pass flow in your nozzle size calculation.

See below document for proper nozzle selection.

Keep connecting fittings like elbows and tees to a minimum. Use PTFE liquid or tape on all connections. Inspect all connections at regular service intervals.

The pressure gauge is the pulse of your system. It will tell you if something is not functioning correctly in your system. No reading indicates the gauges is probably damaged and needs to be replaced. Check pressure with new gauge and replace as needed.

If the pressure is fluctuating, possible system issues could be:

• Poor inlet condition
• Malfunctioning regulating device
• Worn seals and/or valves

Evaluate these items and correct or replace to avoid more serious damage to the pump or system.

Check to see if the regulator and relief valve performance range covers your system performance. If the system spec is out of the valve range, it will not function properly.

The regulating/relief valve may become clogged from debris in the pumped liquid. Check liquid supply for contamination. Inspect the supply tank. The feed line from your supply tank to your pump should not come from the bottom where it can pick up residue.

A worn internal part in the valve such as a piston stem may have become lodged. Clean and service the valve with repair kit on the same schedule as your pump seals. Reset primary valve and secondary relief valve to system pressure.

Seats and valves are wear items and should be replaced periodically. See the attached chart for more information. Replacement valve kits are available and include the retainer, spring, valve, seat and necessary O-rings to complete the maintenance.

Conditions that can accelerate the wear to valves and seats include:

• Abrasives in the liquid
• Excessive heat
• Cavitation
• Starvation
• Harsh chemicals
• Hard water

Refer to your Pump Service Manual for proper installation procedures.

A clogged inlet filter can be a serious issue for your system. Initially pressure may drop, but ultimately serious damage will result due to lack of liquid to the pump.

• Check supply tank for contamination
  • An open supply tank can pick up debris, so we recommend only installing a cover
• Check and clean filters on the same schedule as replacing your seals
  • Your filter cleaning schedule may need to be more frequent, if the liquid being pumped is recycled or dirty
• If pumping extremely dirty liquid, dual filters or larger filters may be necessary
• When using a holding tank, do not feed the pump from the bottom of the tank

Seals are wear items and require periodic replacement. Please refer to the attached chart for proper maintenance schedule information. Seal kits are available and part number can be found on your pump datasheet. Standard Seal Kits include the Low-Pressure Seals, Hi-Pressure Seals and necessary O-rings for standard maintenance.

Typical conditions that accelerate wear to the seals include:

• Abrasives in the liquid
• Excessive heat
• Cavitation
• Starvation
• Harsh chemicals
• Hard water

Make certain the seals are installed correctly. If installed backwards, they will not hold a seal. Refer to your Pump Service Manual for proper installation procedures.

Starving the pump of sufficient liquid to the pump inlet is one of many causes of low pressure. To avoid starving the pump:

• Ensure all valves are open in the supply line before starting your pump
• Check the total demands from the main supply line to assure there is adequate liquid supply when all systems are operating
• Check for line restrictions and minimize elbows and fittings
• Make certain the inlet line is at least the size of the pump inlet port, preferably one size larger
• Avoid Rigid Plumbing 
  • Flexible hose should be installed the last 3-6 feet before the pump inlet.
• When using longer inlet feed lines, a booster pump and a C.A.T. should be considered
• Properly seal all connections with PTFE tape or liquid for air tight connections
• Confirm your liquid temperature is within the maximum limits of the pump
• If temperature are above 130F, a pressurized inlet supply is required
• If returning the by-pass to the pump inlet, install a Thermo Valve in the by-pass line to bleed off excessively hot liquids

When using a supply tank you should also:

• Connect the supply line from supply tank to the pump at least 3-4" above bottom to avoid picking up any sediment
• The pump supply line from the tank should be plumbed from the opposite side of the tank than the by-pass return and tank fill line.
  • This will minimize air bubbles caused by agitation being drawing into the pump.
• The supply tank should contain at least two baffles to help expel air bubbles.
• If returning a high volume of warm liquid to the holding tank, oversize the tank to allow for adequate cooling before going back to the pump.

Check the line size to the pump inlet. It is preferable to use reinforced flexible hose at the pump inlet and eliminate excessive elbows.

An under sized line or collapsing line will starve the pump of liquid. It will give a low pressure or fluctuating pressure reading on the gauge and result in damage to the pump.

Other causes of inlet stress are:

• High inlet pressure from booster pumps
• Spiking return valves
• Rigid plumbing
• Long feed lines

To stabilize inlet pressure under these conditions, install a Captive Acceleration Tube or C.A.T. (Inlet Pressure Stabilizer).

NOTE: the C.A.T. will not function with negative inlet pressure or correct for starvation.

Replace the high pressure hose when it becomes extremely worn or cracked.

Check for damage to the fitting attaching the hose to the system and secure connections with PTFE liquid or tape.

Always use a hose that is rated for the system performance.

Belts are wear items and should be periodically replaced. Check for proper tension. Ensure you are using the correct belt type, length and number of belts to assure adequate horsepower.

Consult you local supplier for belt replacement.

Each pump has a unique crankcase capacity. The amount of oil required is specified on the pump Data Sheet.

Proper lubrication is critical to assure long pump life. Filling the crankcase to the RED DOT on the bubble gauge will assure that adequate lubrication is delivered to the crosshead area of the plunger rods.

Forward rotation is recommended, however, when reverse rotation is necessary, fill the crankcase to midway between the red dot and the top of bubble gauge to assure optimum lubrication is maintained.

Loud knocking noises are most commonly an indication of poor inlet conditions resulting in cavitation. This can be caused by a restriction of the fluid flowing in to the pump, or an air leak on the inlet lines of the pump system.

Review entire inlet section for any potential sources of restriction or air leaks:

• Clogged filter
• Sticking solenoid valves
• Sticking check valves
• Loose hose clamps
• Loose fittings

We also have our Cavitation Whiteboard Sessions videos explaining the causes, and effects of cavitation below:

Loud sucking noises typically indicate the pump is under stressful inlet supply.

• Review the inlet line size and length
  • Inlet supply line should be at minimum equal to the pump inlet ports and preferably one size larger
• Check the demands on the supply line in your facility to assure there is enough supply when all demands are on
• Review the size of your supply tank and be certain it contains at least two baffles and the feed line from the tank is opposite the fill line
• Install the line out to the pump near the bottom for best flow
• Minimize the number of elbows and tees in the inlet line as each is a restriction on the flow to the pump
• Install flexible hose at the pump inlet
• If a booster pump is required to supply adequate inlet pressure, install a C.A.T. to stabilize the inlet pressure.

Screeching noises are typically an indication that belts are slipping. If this occurs at start up, the belts require adjustment. Review the center distance and belt length and adjust the belt tension. Review the belt selection to make certain adequate horsepower is being delivered. Periodically replace belts for optimum performance.

The crankcase oil seals should be inspected each time the low-pressure and high-pressure seals are serviced. Typically the oil seals are replaced from the drive-end and done when bearings and crankshaft oil seals are replaced. The new oil seal should be installed with the "spring toward the crankcase. Prolonged operation with worn low-pressure and high-pressure seals will permit liquid to travel back along the plunger or piston rods towards the crankcase oil seals. Service the seals more frequently to prevent this premature failure of the oil seal.

With a regular maintenance schedule and oil changes, the crankshaft oil seals will not require regular maintenance. Periodically inspect your crankcase oil and crankshaft oil seals. Typically crankshaft oil seals should be replaced with a bearing replacement or if the oil becomes contaminated.

We only recommend the use of Cat Pumps brand oil in any Cat Pump. Our special formulated premium grade, petroleum-based, ISO 68 hydraulic oil contains an advanced additive package to protect against wear, oxidation, rust and corrosion.

With regular maintenance schedule and oil changes, your bearings should not require replacement for many years. Oil leaking around the bearing cover indicates the seal is worn and the bearing should be replaced. If crankcase oil has been severely contaminated, the bearings will be affected. Operating the pump with excessive wear to the seals and packings will result liquid traveling back along the plunger rod. This eventually will attack the crankcase oil seal and permit oil/water mix and contamination of the crankcase oil. CHANGE OIL IMMEDIATELY IF CONTAMINATED. Operation in excessively humid conditions or with direct spray onto the pump may also affect the crankcase oil.

With a regular maintenance schedule, plunger or piston rod wear is not a regular maintenance concern. Prolonged operation with worn low-pressure and high-pressure seals (plunger pumps) or cups and piston rod O-rings (piston pumps) can result in liquid traveling back along the plunger or piston rod and resulting in scoring of the rod. This scored surface will cause wear to the crankcase oil seal and some external leaking. Increasing the frequency of seal servicing will minimize the plunger or piston rod wear.

These items seldom need servicing. Check to see if they are properly tightened. If crankcase oil becomes contaminated, replacing the O-rings on the drain plug and oil gauge is recommended. Exercise caution when installing to avoid cutting the o-ring. Hand torque to specifications in torque chart.

All Cat Pumps oil caps are vented to atmosphere. On many pumps there is a shipping plug installed on the top of the red cap to prevent oil from spilling during shipping. This plug must be removed to allow the crankcase to be vented to atmosphere.

If the shipping plug is not removed, there is a small chance that pressure can build in the pump crankcase during operation and push oil past the oil seals. Remove the shipping plug and wipe clean any oil leaks near oil seals. Fill the oil to the correct level and run the pump again to see if this resolves the issue.

If the blue crankcase has been over-filled, it is possible oil can spray out of the vented red oil cap. Check the oil level in the pump sight glass. It should be filled to the red dot. If it is filled past this, drain some of the oil from the drain plug on the bottom, back of the blue crankcase. Ensure oil level is correct before using.

Using oil other than Cat Pumps brand oil may result in foaming, and frothing of the oil. This can cause the oil to leak out of the vented red oil cap.

Also, if the drive end has been contaminated by the pumped fluid leaking past worn or damaged seals in the pump manifold, the oil level can rise causing oil to leak from the vented red oil cap.

If either of these situations occur, stop use immediately. Drain the oil and inspect the drive end for signs of premature damage, or wear. Replace the seals inside the manifold as required. Clean out the drive end and fill to correct level with Cat Pumps oil.

Pulsations can occur when a restriction in the inlet line or air is drawn in with the liquid. Proper line size and adequate liquid to the pump are critical. Clean inlet filters regularly. Increase your filter size or use dual filters if clogging occurs too frequently. Check all connections and use PTFE liquid or tape for airtight connections. Ensure the line size is at least the size of the pump inlet (preferably one size larger), and elbows are kept to a minimum. A flexible hose is recommended 3-6" before the pump inlet. A properly baffled supply tank will eliminate air from the inlet line. Some liquids require a pressurized inlet and a C.A.T. to stabilize inlet pressure.

This condition is typically a result of liquids that are easily set up, are high viscosity or contain suspended solids. Check supply tank for contamination. Review the viscosity of the liquid. Cat Pumps operate best with liquids up to 500CPS or 2500SSU. Some liquids change in nature by heat, velocity as it moves through the pump, exposure to the atmosphere or blending with other liquids. Some liquids require a flush before dormant cycles to prevent set-up or pump contamination. Review maintenance schedule.

Worn or pitted valves are typically a result of poor inlet conditions, cavitation or starvation. Harsh liquids or excessive heat may also be a cause. Check supply tank for proper size and excessive air bubbles. Supply tank should contain at least two baffles. The fill line into the tank should be on the opposite side as the discharge line out to the pump. Review the pumped liquid for abrasives and install proper filtration. Check the pH of the liquid to be certain it falls within the 5 to 9 range. Check for excessive temperature and install Thermo Valve in by-pass line or increase supply tank size to allow for cooling. On systems above 130 F, pressurize the inlet and install a C.A.T.

We also have our Cavitation Whiteboard Sessions videos explaining the causes, and effects of cavitation below:

Prolonged operation with worn seals can allow the fluid being pumped to rush around the outside of the seal. This may be observed as a pulsation during operation. Inspect and service the seals as soon as possible. Continued use with worn seals can result in erosion of the pump manifold.

Internal erosion of the pump manifold can allow fluid to leak around the seals or valves. This may be observed as a pulsation during operation. Manifold erosion is typically referred to as "Wash-out". 

Wash-out is the erosion (i.e., pitting, scoring) of the manifold typically around sealing surfaces (i.e., low and high pressure seals, valve seat, and seal case) caused by local water quality (i.e., high pH, hard water, sea water), chemicals being supplied through the pump, or lack of timely maintenance to the seals.

Replacement of the manifold and seals is recommended if wash-out conditions are evident.

To minimize wash-out, flush the manifold with fresh water when the pump is not used and confirm the chemical compatibility of your pump manifold and seals to any chemicals you are currently supplying through the pump.

Cat Pumps also offers manifolds made of a washout resistant material. For more information, click the link below:

Long discharge lines can create a water hammering effect when the pump is not properly isolated. Flexible hose at the pump inlet and prior to any hard plumbing in the discharge line is recommended. Install a pulsation dampener on the discharge manifold.

Many systems will have a check valve on the inlet supply line feeding  the pump. If there is corrosion or debris inside this check valve, the pump may experience turbulent inlet conditions. This will result in downstream pulsation. Inspect, and clean or replace the inlet check valve.

Starvation means you are not getting enough liquid into the pump inlet. Starvation is typically caused by restricted inlet lines, excessive demands on supply line, kinked hoses, excessively dirty inlet filters, low or empty supply tank, excessively long feed lines or air bubbles in the liquid. All of these conditions will severely and prematurely wear the seals. If the situation gets too severe, the valves will also show pitting. Determine the cause and correct. Then install a new seal kit or valve kit as needed.

The ceramic plungers offer an extremely durable wear surface. However, harsh chemicals, extremely hard water, excessive abrasives in the liquid and running dry can score the plunger surface. Operating the pump with excessive wear to the low-pressure and high-pressure seals will allow the male adapter to come in contact with the ceramic plunger and score it. Incorporate a more frequent service cycle. Replace the plungers and install a new seal kit. Plungers are sold separately.

Scored Cylinders generally occur when the cups wear and the pump continues to operate. The piston begins to wear onto the cylinder surface. Sleeves score when the inlet seals wear. Both cups and seals should be replaced at the first signs of low pressure. Carefully examine the interior wall of the cylinder each time the cups are replaced. Carefully examine the outer surface of the sleeves at the end of the piston rod each time the seals are replaced. Any roughness or grooves will prematurely wear the cups or seals. Replace the Cylinders or sleeves as needed. Sleeves are included in the Sleeve and Seal Kits. Cylinders are less likely to become pitted or scored and are sold separately.

Maximum inlet pressure for the piston pumps is 40PSI and plunger pumps is 60-70PSI. The special "K" Block-Style pumps have a special manifold that permits high inlet pressures equivalent to the discharge pressures.

Exceeding the rated pump inlet pressure can result in premature wear of the low pressure seals, resulting in external leaks. If your supply line pressure exceeds the pump inlet rating, install a pressure reducing valve at the pump inlet.

Make certain liquid temperature is within pump range. If returning the by-pass back to the pump inlet, install a Thermo Valve in the by-pass line. If the system is in prolonged by-pass or more than 50% of the total capacity is being by-passed, consider installing dual pumps with the second pump coming on with increased demand. Enlarge supply tank to accommodate high by-pass and allow liquid to cool before returning to the pump.

If pumping high temperature fluids, contact Cat Pumps for recommended seal configurations. techsupport@catpumps.com

Always note the order and direction of parts when removing them from the pump to assist in installing the new items. If installed backwards, seals will not hold pressure. PLUNGER PUMPS: always keep the "V" groove or the "Spring" side of the seals or packings towards the liquid or high pressure side. PISTON PUMPS: always keep the NBR or FPM Cups side of the piston assembly towards the liquid or high pressure side.

Many pressure washers will come with an optional accessory installed to make start-up easier. This Easy-Start valve bypasses pump flow back to the pump inlet during startup and closes once the pump is up to full speed. Sometimes the valve sticks open, resulting in a sudden, and possible intermittent loss of pressure.

Review our Easy Start Troubleshooting Tips Video for further assistance in troubleshooting:

If the unloader stem and piston are dirty or worn, the unloader may become stuck in the open position. This will result in a sudden loss of pressure.

Disassemble the unloader to inspect. Clean, or replace parts as necessary.

When the trigger is released on the gun, a check valve inside of the unloader discharge port closes and traps pressure in the hose. The unloader switches to the unloaded position and runs at low pressure until the trigger is squeezed again. .

If a pump has good pressure when the trigger is squeezed, but the engine starts to bog down, or stall when the trigger is released, inspect the check valve inside of the unloader discharge port. If the check valve  is stuck, or worn, it may not seat properly and the unloader will not shift in to the unloaded position. An inexpensive check valve repair kit is usually available for the unloader. Consult the unloader, or pump data sheet (integral unloader) for repair kit information.

It is important to protect the pump from excessive moisture or direct spray. Operation with contaminated oil will cause damage to bearings, oil seals and other drive-end components. If there are any signs of milky, foamy, or white oil, stop using the pump and evaluate for cause of contamination. Then drain the crankcase, clean the drive end, and fill with new Cat Pumps oil.

Prolonged operation with worn seals and o-rings can permit liquid traveling back along the plunger rod and result in scoring of the rod. Operating with a scored plunger rod can cause wear to the crankcase oil seal and ultimately a mixing of oil/water. Increase the frequency of your seal servicing. Operating with contaminated oil can cause damage bearings, oil seals and other drive-end components.

If your Cat Pump is exposed to moist conditions or frequent direct spraying, a ventilated enclosure is highly recommended. A special oil cap protector is available for most Cat Pumps models for added protection in normal cleaning conditions.

A cracked plunger can allow for internal water leakage. This water can be pulled in to the drive end on the plunger/piston rod return stroke. Examine the plunger carefully when installing seals and replace as needed.

Water leaking between the manifold and crankcase can be a result of worn seals or packings. Low pressure is the first sign of worn high pressure seals. Doing maintenance at the early signs of low pressure readings will assure the seals and packings are replaced before they start leaking and eliminate possible damage to other parts of the pump.

In the piston pumps the sleeve and cylinder surfaces should be examined with each seal and cup replacement. If they have become scored or pitted, the seals or cups will wear quickly and could cause leaking. If the small O-rings on the piston rod are worn, they can permit liquid to travel along the plunger rod and result in a scored rod. Increase the frequency of servicing.

In the split manifold pump models, there are adapters between the inlet and discharge manifolds. Examine the o-rings on these adapters when servicing the seals or valves and replace as needed. Exercise caution when assembling. Lubricate external o-rings to avoid cutting or pinching when installed into the manifold chambers. These O-rings are included in the seal kits and valve kits.

The seal retainer pushes against the backside of the low pressure seal, keeping it perpendicular to the plunger/piston rod. If the seal retainer has become warped from heat, or cracked from high inlet pressure, a leak can develop. Inspect the seal retainers and replace as required.

A cracked plunger can allow for an external water leak. This water can be pulled in to the drive end on the plunger/piston rod return stroke. Examine the plunger carefully when installing seals and replace as needed.

Excessive pressure from a failed, improperly sized or missing relief valve will result in severe damage to the pump. Sometimes this excessive pressure will crack or warp the manifold. In other situations the excessive pressure will be transferred to the drive-end of the pump.

Both a primary and a secondary pressure relief valve are recommended in a high pressure system. Leaving liquid in the pump in freezing conditions can also result in a damaged manifold. Flush the pump with a 50% antifreeze/ 50% water solution before storing. If conditions are extreme, a properly vented enclosure is recommended.