Articles for Contractors

All About Unloaders and Which One You Should Use

How to Adjust Your Unloader by Nozzling Your Pump Correctly

First a word about bypass configurations

Pressure washers generally are manufactured with a closed-loop bypass that cycles the bypass water in a small amount from the unloader by-pass port to the inlet port of the pump, and then back to the inlet port of the unloader. This configuration is an accident waiting to happen.

Friction generated by the plungers moving against the packings generates heat that is transferred to the water. Because there is only a small amount of water, the water temperature increases rapidly. When the temperature exceeds about 155 degrees, damage begins to occur to the packings. If allowed to continue, the hot water can damage the plungers in the pump, damage seals in the unloader, and destroy the hoses between the pump and the unloader.

Ideally, machines would either have their bypass plumbed differently, or have a thermal relief valve or switch installed as a safeguard against bypass heat build-up. Because most machines are manufactured in a way that allows this damage to occur, it is wise to change the setup aftermarket. For mobile wash setups that are truck- or trailer-mounted and are supplied by a water tank, the best way to configure the bypass is to plumb it directly back to the water tank. The benefit of plumbing the bypass this way is that it includes the water in the supply tank in the bypass loop.

With a large amount of water in the loop, there isn’t enough heat generated to increase the water temperature enough to damage anything, no matter how long the equipment runs in bypass. Connect a long bypass hose from the bypass port of the unloader, plumbed with a hose barb, and have it terminate at a barb fitting on the water tank. The water tank can be fitted with a small bulkhead fitting on the top, then plumbed with a properly sized hose barb. The bypass hose can be reinforced chemical tubing, hi-spike bypass hose, or garden hose.

The diameter of the bypass hose is determined by the flow of the pump and the type of unloader being used. For pumps that are rated below 6 GPM, a half-inch ID bypass hose is recommended when using a pressure type unloader, and a quarter-inch ID bypass hose is recommended when using a flow actuated unloader. For a pump with a flow rating of over 6 GPM, a three-quarter-inch bypass hose is recommended when using a pressure type unloader, and a half-inch bypass hose is recommended when using a flow-actuated unloader.


Unloader VB10 2Unloader Types:

• Compensating Unloader

The compensating unloader valve is a pressure-type unloader valve with a compensating feature that makes the characteristic pop of pressure that occurs when the trigger gun is opened less severe. The advantage of having this feature is that the unloader functions more like a flow-actuated unloader without the same disadvantages.


Flow Actuated Unloader

K7 07_1A flow-type unloader responds to the stoppage of the water flow between the unloader outlet orifice and the trigger gun. When the trigger gun is open the water flows through the inlet port and out the outlet port, with a small percentage exiting through the bypass port. When the gun is closed, the flow is diverted through a channel that leads from in front of the outlet port to a piston assembly within the unloader body, forcing it to go down. The water is then all diverted into the bypass port. With no check valve holding the pressure from returning into the unloader from the outlet, the pressure throughout the system is relieved each time the unloader cycles. A cycle consists of the unloader supplying water to the outlet and then diverted to the bypass. An advantage of this type of unloader is that when the trigger gun is opened, there is very low pressure in the hose. The pressure then builds for about one second, at which point the maximum pressure is achieved. The smooth transition from low to high pressure is beneficial because it doesn’t have a jarring effect on the operator. A disadvantage is that a flow unloader does not allow an operator to downsize high-pressure nozzles. Because it senses flow, reducing the flow at the nozzle causes the unloader to cycle repeatedly. This type unloader should not be used with a weep gun as leaks will cause it to cycle.


• Pressure Actuated Unloader

AL607Also referred to as trapped-pressure unloaders, most pressure washers use this type of unloader valve. It is the least complicated to use. This valve responds to the amount of pressure exerted on the bypass valve. The unloader uses a seat, ball, and spring. These components control the flow of water into the bypass port. When the operator has the trigger gun open, the water flows from the unloader inlet port to the outlet port, with only a small amount being bypassed. When the trigger gun is closed, the pressure increases as the pump continues to push water out. When the pressure becomes greater than the resistance of the spring, the ball moves off the seat and allows the water to go through the bypass port. The bypass valve opening is aided by a check valve in the outlet port that quickly diverts the water flow to the ball and seat of the unloader. The check valve in the outlet also traps the pressure in the hose giving the characteristic pop of pressure when the trigger gun is opened that is associated with a pressure-type unloader. An adjustment knob or bolt allows adjustment of the springs tension on the ball by either compressing the spring down to create more resistance, or expanding the spring, thereby causing it to exert less pressure on the ball. When the spring is adjusted to create the maximum outlet pressure, little water enters the bypass port. When the spring is expanded, lower water pressure can push the ball out of the way, thus allowing more water to bypass even when the trigger gun is open. This reduces the flow of water to the gun and, of course, the nozzle. Less water being forced through the nozzle reduces the pressure at the nozzle. Here are some advantages. Pressure-type unloaders are less sensitive to flow restrictions than flow type unloaders. This allows various orifice sizes to be used without cycling problems. Rebuilding kits are usually very simple and inexpensive, providing the ball, spring, and seals or gaskets. A disadvantage to this type of unloader is the trapped pressure that creates the pop of pressure when the gun is opened. It can be dangerous when the operator is working from a ladder; it also spikes the pressure within the equipment.

Rules of the Road for Adjusting Your Unloader

If you don’t understand and abide by these rules you may as well not waste any more of your time. Simply go on with what you are doing because we just love selling repair parts!

Rule 1: Know the maximum operating specifications of your pump.

Rule 2: Never exceed those specifications.

Rule 3: Never install a nozzle that allows for exceeding these maximum pump pressure.

Rule 4: Once you have found the perfect nozzle that will give you the exact pressure (and no more), never again touch your unloader. Take the adjusting knob off and throw it away.

Rule 5: Once all of this is complete and you want to lower your pressure simply install a larger nozzle but never a small nozzle that the perfect size that you found by following Rules 1-4 above.

Understanding the reasoning behind finding the correct nozzle for your pump is the first step in knowing how to adjust your unloader as well as extending the performance and life of your equipment.

Regardless of how long you have been in this business, experience has proven that both pressure washer distributors and contractors seldom get it right. If you are one of the ones who understand this article you will eliminate around 95% of your premature failures and downtime.

Let’s Nozzle the Pump Correctly

Let’s say you buy a 5.6-GPM 3,500-psi pump. The first thing you want to do is determine the exact nozzle that it will take to produce these specs. When you look at the nozzle chart it tells you that a 06.0 nozzle is the one you should use. So let’s see if that’s right. Most times it isn’t. Why? Manufacturers have been known to overstate the capabilities of some of their pumps to stay a little closer to their competition. I remember the first car I bought. It was a 6-cylinder, 1964 Dodge Dart with 3 on the tree. What really intrigued me was the speedometer registered 140 mph. Well guess what … get it so far?

  1. Before you start to adjust the unloader, remove your chemical injector and hook up your hose and gun and install that new 06.0 nozzle (or whatever nozzle the chart tells you to start with.)
  2. With the engine running and the trigger gun in the open position slowly turn the adjusting know so that the pressure gradually increases.
  3. Watch your gauge closely and please don’t even think about telling me that you don’t have a gauge because without one you may as well stop reading.
  4. Slowly tune the adjusting knob until you get to the rated pressure of the pump. In this case it is 3,500 psi.
  5. When you get to 3,500 psi turn the adjusting knob a little more to see if the gauge continues to climb. If it does, guess what, you have the wrong nozzle! Install larger nozzles until you find the perfect match. In this case, I would probably try a 06.5 or 07.0.

So now you are going to say ‘but sometimes I don’t want full pressure’ and if this is the case simply install a larger nozzle. Example: Say the perfect nozzle for this particular pump was a #06.0 and you wanted to reduce the pressure. Try installing a #10.0 nozzle or maybe a #12.

Why don’t you want to reduce the pressure by backing off of the unloader? When you do what is actually happening is you are bypassing valuable water to do so. Example: When you bought this pump you wanted both 5.6 gpm and 3,500 psi and by using the above instructions you have already found the perfect nozzle to give you both. But now you have backed off of the unloader to adjust the pressure down to 2,000 psi rather that installing a larger nozzle and in doing so you have reduced your flow dramatically. In this example, you have cut your cleaning time by as much as 40%.

To monitor and maintain your equipment properly you must have a few low cost tools. Here are the ones you will need when nozzling a pump.

  1. A pressure gauge rated at 1.5 times the maximum operating pressure of the pump. Example: a 3,500-psi pump would require a minimum gauge rating of 5,250 psi (or our 6,000-psi gauge, Part No. 1132)
  2. Engine Tachometer: Remember that to achieve the maximum performance of your pump your gas engine must be running at the proper rpm. In the pressure washing industry this is typically close to 3,600 rpm. If you are having problems with your equipment it could very well be because your engine is not running fast enough and through horsepower loss your pump will not perform properly. (Tachometer/Hour Meter Part No. 1429)

Diagnosing Unloader Problems

Start by eliminating possibilities. Examine other components that may be the problem, starting with the easiest. Low-pressure or low-flow. Make sure the inlet water supply is adequate. Inspect for leaks, repair any significant leaks found. Check for clogs in the downstream chemical injector orifice or the high pressure nozzle and remove any debris found. The next step is to shut down the equipment, remove the unloader by releasing the quick connects, and then install a back-up unloader. If the problem is solved resume working and figure out the other unloader when time permits. If the problem persists, make sure the engine is running at the correct RPM. At this point if the problem hasn’t been resolved, begin pump diagnosis.

Adjusting the Flow Actuated Unloader

Adjustments are made with the pressure washer running and the trigger gun closed. Loosen the jam nut and begin the adjustment procedure with the adjusting bolt turned all the way into the unloader body. It should be noted that this is the opposite of the procedure followed for a pressure type unloader. A flow actuated unloaders pressure output is increased as the bolt is screwed out for the unloader body. Turn the bolt one complete revolution at a time, then open the trigger gun and wait five seconds before taking a pressure reading. Continue to adjust one turn at a time and check the results after each turn until the desired pressure is obtained.

Adjusting the Pressure and Compensating Unloader

Adjustments are made with the pressure washer running and the trigger gun open. Unloaders with knob adjustments should have the knob turned out to the maximum amount possible (counterclockwise). Always begin with the spring tension adjusted out (not compressed). If the adjustment is being made with an adjusting nut, loosen the jam nut to allow the nut to turn, and again, start with the nut screwed out so the spring is under very little tension. Turn the knob or nut one full turn in (clockwise) at a time until the desired pressure is reached. Never compress the spring fully because it will produce a damaging pressure spike when the trigger gun is closed.

Unloader Repairs

Let’s examine if repairing the unloader makes sense. Experience has shown that rebuilt unloader valves do not have as long an operational lifespan as a new unloader. Parts around those included in the rebuild kit wear also, causing the replaced parts to fail sooner. While it isn’t possible to determine how many hours a new unloader or a rebuilt unloader will function prior to failure, knowing that the rebuilt unloader will fail sooner is one consideration in making the decision between new and rebuilt. The other factor is rebuild kit cost verses new unloader cost. If a new unloader costs $35, and the rebuild kit for it costs $29, rebuilding seems foolhardy. But, if an unloader sells for $50, and the rebuild kit sells for $14.95, then rebuilding is probably cost-effective. One other point, unloaders have an unpredictable life span. They can develop a problem when brand new, or they can last many thousands of hours without any trouble. Most unloaders fail somewhere between these two extremes. The age of the unloader should be considered when looking at replacement or rebuilding. A 2-week-old unloader that is leaking where the adjustment bolt is threaded in should probably be rebuilt, while a five-year old unloader should be replaced, and buried with honors.

Unloader Installation

There are a variety of ways to install an unloader. Keep in mind that easy access for adjustment in important. Since unloaders will — not often but — eventually wear out, the use of European style twist fast quick connects allows for rapid and easy replacement in the field. It is recommended that all the ports be set up with quick-connect couplers and plugs. A pressure gauge that is visible when adjusting the unloader is important for precise adjustments. Be sure to properly identify the ports, they are usually marked in, out, and bypass. If they aren’t marked and you don’t know, find out before proceeding. Some unloaders have more than one inlet port to allow flexibility during installation; others have an additional port for a pressure gauge. Unloaders can be mounted directly to the outlet port of the pump using a pipe nipple. There are advantages to mounting the unloader on the pressure washer frame using an unloader mounting block. The unloader can be located where it is the most accessible. A short length of high-pressure hose, which is also called a jumper hose, is used to connect between the pump outlet port and the unloader mounting block. A jumper hose is used to connect the unloader outlet to the inlet of the coil or to the outlet of the pressure washer. Most unloader valves can be mounted vertically or horizontally.

As always, remember to Power Through!

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