Pump Basics
Maintenance Log

Q. I have a General Pump TS1011, what type of unloader/pressure regulator should I get? (the one on there is leaking water!) And what pressure should I set it at?

A. Such innocent questions.... Here goes.


Im going to start with the easiest question first. The horsepower available and the lowest pressure rating of any component limit the pressure setting. This means that the lowest rated component is the highest rating of the system.

The TS1011 pump is rated to 2000-psi at 4gpm but I dont know the ratings of the other components. The ability of the pump to reach the 2000-psi is controlled by the engine/motor. At full flow you need about 5.5-hp electric or 9 hp gas to get the rated pressure at the rated flow. If you can give me the following information I can tell you the potential of your system:

Gas or electric?
Motor RPM?
Direct Drive or belt drive?
Pulley sizes if applicable.

Next question...

There are several factors that determine which components to use on a pressure washer. In choosing an unloader you must consider the Intended purpose, operating conditions, and additional accessories. Doing so will help ensure that the unloader will last and give you the intended results. First a basic understanding of a pressure washer is necessary.

A basic pressure washer system consists of a drive, pump, regulator/unloader, hose, gun, wand, and a nozzle. The motor and pump convert horsepower to water flow to be delivered to the nozzle. Ultimately, the pressure in the system is created at the nozzle as water is forced through the orifice, which is controlled by the unloader. The unloader regulates pressure by either sending water to the nozzle or to bypass depending on the setting of the unloader. The unloader acts as a traffic cop for the system by reacting to the system pressure and directing flow either to, or away from, the nozzle. The more water through the nozzle or the smaller the orifice the more pressure you get, conversely, less water through the nozzle or larger orifice yields lower pressure. When the trigger gun is shut off the traffic cop puts up barricades and directs the flow through the detour we call bypass. Just like drivers on the road, the water circulating in bypass heats up if it is left there too long.

If the spring tension on the unloader is set low, pump pressure will be low because water is bypassing the nozzle. Increasing spring tension on the unloader will direct the flow to the nozzle and increase the operating pressure until there is no more flow to go to the nozzle. Can you guess what happens as the nozzle wears? A worn nozzle has an oversized orifice, so pressure will drop. What do you think happens if you adjust the unloader to a higher pressure setting with a worn nozzle? Remember that the unloader directs flow and that all of the flow was already going to the nozzle. In this case the operating pressure wont increase but the amount of pressure it takes for the unloader to unload (traffic cop to put up the barricade) will.

Look at it this way: At a low pressure setting everyone is wearing roller skates, which can change direction very easily. As you increase the pressure setting the vehicles change from roller skates to bicycles to compact cars to buses to semi-trucks to freight trains. Imagine how hard it would be to stop or redirect a freight train compared to a compact car. This is the concept of pressure spike.

A spike of pressure occurs when the unloader shifts modes (changes the direction of the water) from spraying to bypass. The spike pressure increases with the unloader setting until it becomes so great that damage begins to occur in the system broken hoses, blown valve caps, leaking unloaders and so on. The spike pressure increases with the size of the vehicle. The pipeline is the same and the flow is the same but the roller skates have become freight trains.

Proper unloader setting allows a small amount of continuous bypass (approximately 5% of total flow) to minimize the pressure spike and compensate for nozzle wear. As the nozzle wears the 5% bypass will be redirected from bypass to the nozzle allowing for a longer operational period before pressure begins to drop. As soon as a pressure drop is noticed the nozzle should be replaced. Once an unloader is set it should never have to be adjusted again unless there are modifications done to the system.

There are two main types of unloaders used on pressure washing equipment, pressure trapping and flow actuated. Pressure trapping unloaders react only to pressure in the system and give you instant pressure when you open the trigger gun. Flow actuated unloaders react to both flow and pressure and give you a gradual build in pressure sometimes referred to as a soft start.

Speaking in terms of intended use (application), a pressure trapping unloader is most appropriate when you are working on very durable surfaces I.E. Metal, concrete, brick, and asphalt. The sudden burst of pressure is less likely to damage these surfaces but beware if you are working on a ladder, you can lose your balance. The flow-actuated style is appropriate for more delicate surfaces such as glass, wood, limestone, asphalt, plastic and so on. Also the soft start is better for working in precarious locations. The pressure builds gradually (over about one second) so you have a better chance to maintain you balance. I have to say that following OSHA guidelines when working in elevated locations is strongly recommended.

Operating conditions affect the unloader because water quality, temperature, and time in bypass effect life and reliability. The conditions effect both types of unloaders equally inasmuch as poor water quality and extended bypass will wear them both out but one type of unloader is more expensive to repair and/or replace. On average a pressure-trapping unloader is about one quarter the cost of a flow actuated to repair or replace. Another consideration is that the pressure-trapping unloader is more forgiving as it wears out. It will usually continue to operate to some degree even as it is near complete failure. Flow actuated unloaders are slightly more finicky and may cease to function if they wear too much out of tolerance.

Finally, additional accessories such as more discharge hose, injectors, speed controllers, burners, telescoping wands and certain types of nozzles affect the unloaders differently. Pressure trapping unloaders respond to the pressure in the system. Additional accessories increase the apparent pressure and a pressure-trapping unloader will just bypass more water to regulate pressure. With a flow-actuated unloader changes to the system can effect the operation of the unloader. Any line restriction downstream of the unloader will change the Flow -actuated unloaders operating characteristics.

After reading this it may sound as if I am pro pressure-trapping unloaders and against flow-actuated. Actually my preference is flow actuated because it is easier on the system over-all. Pressure-trapping unloaders offer a little more reliability over flow actuated but once the system is setup correctly a flow actuated unloader is as reliable if not more so than a pressure trapping.

Look at the ZK7 series unloaders and the Pulsar3 unloaders both are excellent in design and operation and will provide you years of use if properly installed and maintained. .


Q. We have been experiencing some very odd problems with our pressure wash system. The problem is the system intermittently seems to cause an over current condition, and causes a 20 Amp breaker on the supply line to pop? When the breaker is reset every thing appears to be fine until it happens again, at random. Any suggestions?

A. Not a problem...

The unloader is a valve that directs flow to either the nozzle or to bypass.  

Pressure is developed in a pressure washer system as a result of forcing a constant volume of water through a fixed orifice (nozzle). This is accomplished by the use of a positive displacement pump such as the TS1011. A positive displacement (PD) pump displaces a precise amount of liquid for each revolution of the crankshaft and must be allowed to pump if it is running. In other words, If the pump is turning it will be moving water and stopping the flow with the pump running would be called dead-heading. If you dead-head a (PD) pump there is a good chance something is going to break there is no internal means for allowing water to slip by the pumping elements (plungers). Consider that the PD pump is capable of generating an infinite amount of pressure (at least until something breaks). On the minor end you may damage the pump or motor, hose or gun. On the extreme end, dead-heading can cause personal injury or death. This is the reason an unloader/regulator is required. We strongly recommend installing a safety relief valve in addition to the unloader to add more protection from dead-heading.

The unloader is controlled by flow or pressure (depending on the particular type of valve used) and protects the system from over-pressurization. Should a nozzle begin to clog, or some other restriction in the discharge form, the unloader/regulator will senses that the system pressure is rising beyond a predetermined value and it will divert enough liquid to bypass to maintain its preset pressure. In the event the trigger gun is completely closed it will divert 100% of the pumps flow to bypass.

Typically, the unloader is mounted directly on the discharge side of the pump. Follow manufacturers instruction regarding the installation and adjustment of any unloader and safety relief valve you choose. Never exceed the maximum pressure or flow ratings of any component in your system the component with the lowest rating determines the maximum performance available from your system.

Q. I bought a 6000 psi gauge and put it in-line across from the spring on the unloader valve, backed off all spring pressure, and started the 18hp Honda engine. I slowly adjusted the spring tension to its max which turned out to be only 2800 psi on a 4000 psi pump. While running, trigger squeezed, it seemed OK , but activate the unloader by releasing the trigger and the unloader shaft slowly(about 3 seconds) moves out then jerks in peaking pressure over and over until the trigger is activated again.

Now my problem is low pressure (2800 psi) and surging peak pressure through the unloader valve. I tried to purchase another unloader but my distributor doesnt carry the correct replacement.

Is this what I need to replace at this time?

A. There are a couple things going on here. I dont think the unloader is the problem. First, it seems that the nozzle in the system is too worn or too large for you to get full pressure. Second, there is a leak in the system that is allowing pressure to bleed off when the unloader is put in bypass.

The nozzle: The nozzle is what actually creates the pressure. The amount of pressure you get is directly related to the flow delivered by the pump and the size of the orifice (hole) in the nozzle. So, the smaller the hole the more restriction and more pressure. Nozzles wear as they are used. Eventually the orifice gets too large to create the proper amount of restriction. I am guessing here but lets say you have a 4 gal/min pressure washer, in order to get 4000 psi you need a #4 nozzle. Take a look at the spray tip and write back to me with the markings you find on the tip. Also, let me know what model pump and how many GPM the pump is pumping.

The unloader: The unloader that you have serves two functions, a regulator and an unloader. In its regulator function the unloader controls the system pressure by controlling the amount of water that flows to the nozzle. (Remember that pressure is created by forcing water through the orifice. The more water forced through a fixed orifice the more pressure. So less water means lower pressure.) It does this by opening an internal valve based on the system pressure and the spring tension set on the valve. As the pressure in the system overcomes the spring tension, water is diverted from the nozzle back to the inlet of the pump where it is recirculated. As an unloader it does essentially the same thing except that when you close the gun the unloader traps the pressure in the hose and locks the unloader open, allowing all the water the pump is pumping to recirculate back to the inlet. This is called unloading. If the trapped pressure bleeds off the unloader will cycle, or hunt. Look for any signs of leaking between the gun and the unloader valve. It may be leaking through a defective chemical injector, fitting, or ruptured hose. If you do not have any leaks it is possible that the unloader may be leaking internally but lets look for the obvious leaks first.


Q. How do I calculate the horsepower required for my system?


A. The horsepower required for operation is based on three variables: discharge volume, pressure and drive type. The formula for the calculation is H=(P*G)/C.

 Where:         H = Horsepower

   P = Pressure in PSI   

    G = Flow in GPM    

    C = Drive constant:    

    Hydraulic C         

    Electric C          

    Gasoline C         C= 1250 (Industrial grade )

    Gasoline C         C= 1100 (Standard grade)

    Diesel C     C= Supplied by Engine Mfr.

This will give you an estimate of the horsepower required for the system. To specifically determine required horsepower, motor and drive efficiencies must be considered. Contact your motor supplier for these values.


Q. How do I size nozzles for a multiple Medical Equipment system?


A. Sizing nozzles for a multi-gun system is similar to sizing them for a single gun application. Divide the total flow by the number of guns and size the nozzle according to each gun抯 flow and desired pressure. Be careful not to exceed the system ratings.


Q. What kind of oil do I use in my General Pump?


A. Inter Pump specifies IP Series Oil X-9.9(SAE  15W40 Mineral ) in all 44, 47, 49, 50, 51, and 57 series pumps. If your pump is not in one of these series, or if your application requires that the pump be run continuous or exceeding normal ratings please call 800-8574-687 for alternate lubrication requirements.
Q. At what RPM should I run my general pump to achieve a desired flow?

                   A. Required RPM can be calculated if the ratings are known.

                   The formula for calculating required RPM is as follows:


Where:         这里:
RPMR = Rated RPM     额定的转速
GPMR = Rated GPM     额定的流量 GPM
RPMD = Desired RPM   所需的转速
GPMD = Desired GPM   所需的流量 GPM

Q. I have a rattling noise coming from the backend of my pump while it is under load. What is  happening?

 问题 当运行后,水泵背部发出卡塔卡塔的声音。发生了什么?

A. The sound you are hearing may be the pump cavitating. Ensure that the pump has adequate oil and that all drive components are tight. Check all supply lines and filters for obstruction and ensure that you have an adequate supply of water to the inlet of the pump. If you have upstream chemical make certain that the lines are filled with product and not leaking. Leaks in chemical lines or inlet plumbing indicate a possible source of air in the system.

Q. Im noticing water in my oil. Do I need to replace my oil seals?

A. Water in the Indium oil usually indicates a water leak unless the oil seals are leaking oil they are all right. Examine the pump for signs of water leaking from the manifold. If no water leaks are evident, change the oil and run the pump. If the oil clouds up immediately it may be that the oil is foaming. If you are not using IP oil make sure you are using the proper weight non-detergent oil for your application.

For fast answers to your questions, contact:


                       Tony Chen

                       Sales Engineer


© Interpump Group - All rights reserved - Free Hot Line:800-8574-687 Help - Contact us - Credits   design by :haodi network我要啦免费统计