12 / 11 / 2021

What Causes Hydraulic Pump Whine?

What does it mean when your hydraulic pump starts to ‘whine’? This blog covers the reasons why your pump may be faulty, and how to diagnose & correct the problem.

Abnormal noises coming from a hydraulic pump should never be overlooked. Every type of hydraulic system makes some noise when operational – but if that noise suddenly rises to an unusually high level, or the sound it makes starts to change, that can be a problem.

By design, hydraulic pumps will generally muffle most of the sound produced by the liquids coursing through the system. This means that the sounds emitted from the system should stay more or less constant.

When you are dealing with a malfunctioning pump, this may not be the case. Any issues within a hydraulic system are usually simple to detect and will typically present itself in the form of a high-pitched whining, whistling, clicking, or banging sound.

If you’re experiencing hydraulic pump whine or abnormal noises coming from your system, detection and correction are crucial at the earliest stages. Whilst the noise may not seem like anything more than an annoyance, it can indicate a serious system problem which requires attention immediately.

There are typically two main causes behind hydraulic pump whine: cavitation and aeration. It can be difficult to differentiate between the two as they produce similar signs, but correct diagnosis is crucial to finding the most suitable solution.

The purpose of this article is to help you identify the signs that your hydraulic pump may be failing, what is causing it, and how it can be corrected & prevented in the future.

Hydraulic pump whine caused by cavitation

Cavitation is one of the most common causes of hydraulic failure. It can happen anywhere within the system, but is usually found at the pump.

hydraulic pump cavitation

Hydraulic pump cavitation. Image source: Wiki

Causes of pump cavitation

Pump cavitation is first and foremost caused by insufficient flow. This happens when the volume of fluid being supplied doesn’t meet the demands of the hydraulic circuit, and the pressure at the suction end of the pump isn’t sufficient. This leads to the absolute pressure falling below the vapor pressure of the liquid, which leads to air bubbles being formed. These tiny bubbles implode as they pass through the system, creating shockwaves and causing pump vibrations.

The process of these bubbles forming and collapsing is done with a great deal of force, and leads to eventual metal erosion inside the pump. The mechanical damage caused by cavitation can have irreversible impacts on system components and may possibly lead to complete failure. Cavitation happens only on the suction side of the pump, and may be caused by a series of different malfunctions, including:

  • Too little oil
  • Cold oil
  • Excessive suction at the pump
  • Narrow suction pump
  • Collapsed oil strainer
  • Pump too far above the oil level

Signs of pump cavitation

Cavitation is typically characterised as a high-pitched whining or screeching sound, and in some extreme cases, can present itself as a loud rattling sound. Whilst these hydraulic pump whine noises are generally the most obvious telltale signs of cavitation, other symptoms to look out for also include:

  • Unusual vibrations
  • Failure of seals or bearing
  • Erosion of the pump impeller
  • Decreased flow or pressure
  • Higher power consumption than usual

Hydraulic pump whine caused by aeration

By design, hydraulic pumps contain a miniscule amount of air which allows space for the hydraulic fluid to heat up and expand. However, too much air in the pump can cause serious issues – this is known as aeration.

Causes of pump aeration

Aeration in a hydraulic pump occurs when there is an air leak in the suction line. When outside air enters the pump through a damaged connector, loose pump seal, pipe fitting, or any other damage, it gets drawn into the pump’s hydraulic fluid supply. This unwanted air quickly gets dissolved into the hydraulic fluid and leads to contamination.

Contaminated hydraulic fluid can have serious implications for the system, as the excess air means that it cannot conduct heat as efficiently and can cause the fluid to foam. This can lead to overheating and in some cases, a substantial decrease in power. Aeration may happen on both sides of the pump, and has several causes including:

  • Broken pipe seals
  • Oil level below the suction line
  • An opening anywhere in the pump

Signs of pump aeration

Similar to cavitation, aeration is usually indicated by a sudden change in noise, which can sometimes make it difficult to differentiate between the two causes However, aeration tends to produce a more erratic low-pitched ‘rumbling’ or ‘rattling sound, as opposed to the more consistent whining noise of cavitation.

hydraulic pump diagram

How to prevent hydraulic pump whine

Hydraulic pumps are robust pieces of equipment and in most cases, can last through years of service. However, this does not mean that they aren’t vulnerable to mechanical issues.

Any of these problems can arise through years of wear and tear, or suddenly from a failure in the system. Cavitation and aeration can cause catastrophic damage to hydraulic systems, but can be prevented for the most part by ensuring that your pump is properly maintained.

To get the most out of the duration of your pump’s lifespan and prevent hydraulic pump whine, perform regular maintenance checks and monitor your system for any of the following warning signs:

  • Loose connections or fittings on the suction line
  • Restriction of the fluid flow to the pump
  • Damage or wear and tear to the pump
  • Hydraulic fluid foaming or incorrect temperature
  • Excessive pump speed

It goes without saying that the most effective way to prevent any damage to your hydraulic system is to ensure that you choose the right pump and components for the application.

Primary Fluid Power stocks a wide range of hydraulic pumps and spares from Eaton Vickers, Roquet, Rickmeier and Marzocchi. We offer unrivalled technical support, should you require any assistance in regards to choosing the right pump, or have any concerns regarding your current set up.

If you can’t find the exact pump you are looking for, we are fully equipped with the in-house facilities needed to assemble complete components. Through our bespoke service, we can build and modify hydraulic pumps to meet the requirements of your application.

Can’t find what you are looking for? Our technical team is on hand to help. Simply get in touch with us online or call us on 0151 632 9500.

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