Hydraulic cylinders are just about everywhere, from equipment to auto components. Prolonged use or operational errors will ultimately introduce air into the system, resulting in inefficiency, irregular movement, or breakdown. The problem is that the majority of hydraulic systems lack dedicated bleed valves, so it is truly essential to learn how to bleed air from hydraulic cylinders without a bleeder valve.
Why is air bleeding critical for hydraulic cylinders?
When you run a hydraulic cylinder, its power is actually coming from the fact that hydraulic fluid is essentially incompressible. This allows pressure developed by the pump to be transmitted to the piston in a manner that gives you reliable operation. But if there is air in the system, all of this changes. Air is compressible, so there will be delayed movement, inefficiency, and even shutdown. To get your hydraulic cylinder operating smoothly with consistent strong operation, you have to bleed this air out.
How does air get into hydraulic cylinders?
There are many reasons for air getting into hydraulic cylinders, mostly due to leaks, temperature changes, and improper operation.
Leakage
In fact, even a very small gap in the hydraulic system allows air to “creep” into the cylinder, particularly at seals or joints.
Improper Operation
When you add or change hydraulic fluid improperly, it is simple for air to get into the system along with the fluid.
Temperature Changes
During equipment operation, significant temperature changes can cause air dissolved in the hydraulic fluid to be released, finding its way into the lines and cylinder body.
What occurs when air gets into a hydraulic cylinder?
When air enters a hydraulic cylinder, its impact is generally worse than you imagine. Some of the common issues are:
Deterioration of hydraulic fluid: Air entry forms bubbles that are constantly burst under high pressure, which causes foaming and accelerates oxidation.
Efficiency loss: Hydraulic systems rely on the incompressibility of fluid to transmit pressure. Air, however, is compressible, and it causes the system to consume more energy to perform the same work.
Unstable operation: As the piston moves through air-contaminated regions, resistance changes randomly, causing equipment to jerk, stall, or even lose control.
Component wear: The presence of air breaks oil lubrication and increases impact forces. Seals and other parts wear out faster over time, resulting in shutdowns in extreme cases.
For hydraulic equipment manufacturers, precision machined parts are also important to maintain accurate assembly and reliable system performance.
Therefore, if you suspect air has entered the hydraulic cylinder, bleed it out immediately to prevent minor issues from escalating into catastrophic failure.
How to Detect Air in a Hydraulic Cylinder?
When air enters the hydraulic cylinder, you’ll typically notice the following signs:
Slow Movement
Once air absorbs pressure, the piston lacks sufficient thrust, and mechanical actions noticeably slow down.
Vibration
The cylinder extends or retracts unevenly—varying speeds or even jerking—are typically an indication of air compressing and decompressing internally. Further operation in this manner can accelerate internal component wear.
Noise
A good hydraulic system makes smooth sounds. But with air in the system, you’ll hear strange “clicking” or “hissing” noises—bubbles constantly imploding within the oil.
Temperature Rise
When the hydraulic cylinder is excessively hot to the touch, this is most likely due to air being repeatedly compressed under high pressure, causing heat buildup.
Bubbles
If you see bubbles in the hydraulic fluid, there’s no doubt about it—this is a definite indication air has entered the cylinder.
What should you do before bleeding the system?
Before you actually bleed the system, you must complete all the preparatory steps. The right tools and proper protective gear ensure a smoother and safer process.
1. Tool Preparation
Minimum tools required are a wrench, oil absorbent pads, and a clean receptacle for catching drained fluid. It’s also a good idea to have some new hydraulic fluid available to top up any lost quantity. Replace the fluid completely if it is contaminated or emulsified.
2. Safety Precautions
Wear safety goggles and protective gloves at all times. Bleeding is usually accompanied by oil splashes. Gloves minimize skin irritation, while goggles safeguard against accidental contact of oil droplets with your eyes. This guards against minor injuries during the procedure.
3. Safety Precautions
- Release System Pressure: Initially, shut off the hydraulic pumpand slowly relieve any pressure still remaining in the system. If the system remains under pressure, even opening a small fitting can cause high-pressure fluid to spray out—extremely dangerous.
- Ensure Ventilation: Work in a well-ventilated area. Hydraulic fluid gives off strong mist once these fluids are in use. Ventilation dissipates these fumes so rapidly that its health effects are minimized.
- Avoid Flame Sources: Open flames and smoking should be entirely avoided during venting. Hydraulic fluid poses a fire hazard when heated or sprayed, thus maintain a workspace free from flames.
How to Bleed Air from a Hydraulic Cylinder Without a Bleed Valve?
The majority of hydraulic systems lack individual bleed valves, and you must use other methods to remove air. Proceed with the following steps in sequence:
Step 1: Locate the Hydraulic Cylinder
Locate the hydraulic cylinder first and examine the fittings on top of the cylinder. Air will typically accumulate at the top, which is the most accessible location.
Step 2: Loosen the Fitting
With the system at low pressure or shut off, slowly loosen the fitting in such a manner that air will escape along with the fluid. Work cautiously—avoid abrupt, excessive loosening, which can cause fluid spraying and thereby waste and potential dangers.
Step 3: Perform Reciprocating Motions
With no load on the hydraulic cylinder, cycle it through several complete strokes. This will discharge trapped air from the reservoir.
Step 4: Monitor the Reservoir
Watch for bubbles in the reservoir fluid. They indicate air being expelled. Recycle the motion; you’ll notice the bubbles gradually vanish.
Step 5: Adjust Angle
In case there is still air, attempt to alter the cylinder’s angle slightly and repeat Steps 3 and 4 to expel trapped gas. Omit this step if your cylinder is position-fixed.
Step 6: Tap the Cylinder
For stubborn bubbles, gently tap or shake hydraulic lines during low-pressure running of the cylinder to expel trapped air. Avoid using forceful means to prevent damage to components.
Step 7: Replenish Hydraulic Fluid
Fluid loss might occur during bleeding. Check and top up hydraulic fluid upon completion. If fluid is noted to be emulsified or contaminated, replace it first.
Step 8: Test Run at Low Speed
Following bleeding, don’t resume normal operation right away. Operate the hydraulic cylinder at slow speed for some time, pausing at the stroke end for several seconds. This permits trapped gas to accumulate and be driven out.
How to ensure that all the air has been driven out of a hydraulic cylinder?
There is no hard and fast rule to determine whether all the air has been bled. You can, however, determine it by looking at a series of indications:
No bubbles
Look at the reservoir while bleeding. If no more bubbles are rising, the majority of the air has been bled.
Noise reduced
When air is present in the system, there is knocking and gurgling. Once all air is purged, nothing but normal pump sound and mechanical function can be heard.
Temperature is restored to normal
When you work with the cylinder body and piping and discover the temperature is considerably lower, this indicates air has been purged, too.
Smooth operation
The most obvious indicator is the movement itself. The air-free hydraulic cylinder will glide effortlessly, eliminating speed wobble or sudden jerking.
How is air prevented from entering the hydraulic system under normal usage?
When working with hydraulic equipment, not only will air present interfere with efficiency, but, in certain situations, can even contribute to system failure. Aside from keeping them in regular maintenance, you can also adopt simple habits during normal operations to reduce hazards.
- Inspect for leaks on a regular basis
Keep an eye on the pipes and fittings, especially the bends and seals, as they are easy to leak. In case you notice leaking spots, address them immediately so that air cannot enter.
- Inspect the hydraulic oil level and purity
Ensure hydraulic oil is always at the marked level. In case the oil level drops below the minimum, the hydraulic pump will suck air directly into the system, and it will be there permanently. Do you notice any color change of the oil? Any indication of emulsification or degradation means it must be replaced right away.
- Check and tighten fittings
Equipment vibrates while being operated, and the fittings loosen their grip occasionally. From time to time tightening the fittings is very easy to prevent air from entering the system via gaps.
It takes time to follow these small habits, but these can help considerably in reducing possibility of air entering the hydraulic cylinder, which will help in avoiding downtime and additional repair costs for you.
Conclusion
Bleeding hydraulic cylinders is a critical hydraulic system maintenance task. In addition to slowing down a system, air intrusion can cause downtime. Lack of a pressure relief valve specifically for bleeding introduces an added level of complexity to the process. It is therefore crucial that you understand how to bleed cylinders without a pressure relief valve. It allows you to purge air out of the system in a matter of minutes, hence conserving downtime and repair money.
If you have queries regarding how to bleed without the use of a bleed valve, you are free to contact our technical department. We shall provide you with a convenient, reliable, and one-stop solution that best meets your needs.
FAQ
What type of hydraulic oil needs to be added during refilling?
This is dependent on your model of equipment. The best is to adhere strictly to the manufacturer’s specifications for hydraulic fluid. Random substitution can lead to incompatibility of seals, lubrication failure, or even system destruction.
Why do bubbles form when bleeding a hydraulic cylinder?
This is as a result of air being drawn into the system being compressed and expanded repeatedly in the hydraulic fluid to create bubbles. Bubbles are released upon opening fittings or when operating the cylinder.
Is it normal to lose hydraulic fluid during bleeding?
Yes, it is normal. You typically do experience some fluid loss with bleeding. As long as you inspect and refill the oil level right away after the procedure, it will not affect system performance.
How often should I bleed the hydraulic system?
No time schedule is required. You have to decide based on the performance of the system. For example, when you notice jerked movement, abnormal noise, or extensive overheating on running in the hydraulic cylinder, these are signs that air could have found its way into the system. Bleeding has to be performed at such moments.
