1. What type of unloader/pressure regulator should I get for my pump? At what pressure should I set it?

The pressure setting is limited by two things: the horsepower available and the lowest pressure rating of any given component. This means that the lowest rated component is the highest rating of the system.

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 like a traffic cop for the system by reacting to the system pressure and directing flow either toward 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 a 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 won’t increase but the amount of pressure it takes for the unloader to unload (traffic cop to put up the barricade) will.

To illustrate this idea: a low pressure setting is similar to everyone 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 systembroken 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.

A 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 as you could 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 your balance. Follow OSHA guidelines when working in elevated situations.

Operating conditions affect the unloader because water quality, temperature, and time in bypass effect life and reliability. The conditions affect both types of unloaders equally, inasmuch as poor water quality and extended bypass will wear them both out. Note that, 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 affect the operation of the unloader. Any line restriction downstream of the unloader will change the flow-actuated unloader’s operating characteristics.

Flow-actuated unloaders tend to be easier on the system overall. Pressure-trapping unloaders offer a little more reliability over flow-actuated, but once the system is set up 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.

2. Our pressure wash system seems to intermittently cause an over current condition, and causes a 20 amp breaker on the supply line to pop. When the breaker is reset everything appears to be fine until it happens again, at random. Any suggestions?

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. 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, the motor, the hose or the 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 sense that the system pressure is rising beyond a predetermined value. It will divert enough liquid to bypass to maintain its preset pressure. In the event that the trigger gun is completely closed it will divert 100% of the pump’s flow to bypass.
Typically, the unloader is mounted directly on the discharge side of the pump. Follow manufacturer’s instructions 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.

3. 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, with trigger squeezed, it seemed OK, but when I activate the unloader by releasing the trigger, 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 doesn’t carry the correct replacement.
Is this what I need to replace at this time?

There are a couple things going on here. The unloader may not be 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 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.

The unloader that you have serves two functions—as a regulator and as 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 that 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 look for the obvious leaks first.

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

The horsepower required for operation is based on three variables: discharge volume, pressure and drive type. The formula for the calculation is:
H = Horsepower
P = Pressure in PSI
G = Flow in GPM
C = Drive constant
Hydraulic C = 1714
Electric C = 1460
Gasoline C = 1250 (Industrial grade)
Gasoline C = 1100 (Standard grade)
Diesel 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.

5. How do I size nozzles for a multiple gun system?

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’s flow and desired pressure. Be careful not to exceed the system ratings.

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

General Pump specifies GP Series 100 oil 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 continuously or exceeding normal ratings please call 888-474-5487 x199 for alternate lubrication requirements.

7. At what RPM should I run my general pump to achieve a desired flow?

Required RPM can be calculated if the ratings are known.
The formula for calculating required RPM is as follows:
RPMR = Rated RPM
GPMR = Rated GPM
RPMD = Desired RPM
GPMD = Desired GPM

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

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.

9. I’m noticing water in my oil. Do I need to replace my oil seals?

Water in the 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 GP oil make sure you are using the proper weight non-detergent oil for your application.

For fast answers to your questions, contact:

Mark Veldman

Customer Service/Inside Sales Manager

General Pump

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