One of our readers wrote to me recently about the following concerns:
"Are there any specific considerations I should be aware of prior to replacing pumps and motors on an excavator with aftermarket units? If I order a pump from a supplier other than the OEM, how can I be certain that the pump I'm getting is precisely the same as the one I'm replacing?"
This is a good question. In fact, I devote a whole Chapter to this topic in my book Insider Secrets to Hydraulics.
A machine owner will usually get a better price on a replacement hydraulic component if they are able to buy it 'aftermarket', from a fluid power distributor. However, this is not always as easy as it might seem. Original equipment manufacturers (OEM's) usually do all they can to control the distribution and sale of spare parts for the machines they build. This is particularly true in the case of mass-produced hydraulic machines. The OEM knows that if you can identify the make and model of the hydraulic pump fitted to your excavator, you will be able to shop around for the best price on a replacement pump and as a result, there is a good chance they will lose the business.
In an effort to prevent this from happening, OEM's usually identify hydraulic components fitted to their machines with their own part numbers. In most cases these numbers are meaningless to anyone else. Therefore the first thing you need to do is to identify the component's manufacturer and model code.
If you know another operator or company that owns the same machine you need the replacement component for, you could ask them if they have replaced this component with an aftermarket unit. If so, they will probably be happy to give you the model code from the aftermarket component's identification tag.
If you have a good idea of what you're looking for, you can identify the component yourself, using information that is available on the Internet. This involves first measuring and identifying the component's physical attributes such as shaft type, mounting flange, ports, displacement and control. You then need to match these variables to the dimensional and technical data contained in the manufacturer's product catalog. The catalog will show you how to compile a model code (sometimes called an order code) that corresponds to the component you want to replace. Sounds easy, but if you don't know who the manufacturer is or what the component does, this can be a difficult task. In this case, it is easier to let a fluid power distributor do the work and earn their profit margin in the process.
It is not always possible to source aftermarket hydraulic components for OEM equipment. OEM's sometimes use components that are manufactured with a unique difference, known as 'OEM specials'. This means that even if you do identify the make and model of the component, the only way you can buy an identical unit is through the machine dealer.
The difference may be something obvious, such as the shaft type or the orientation of the ports - or not so obvious, such as the control set-up in a variable displacement pump or motor. I can think of at least one example where the main pump for a particular excavator was, to the casual observer, a standard unit. However, if a pump from the component manufacturer's standard product line was installed on the machine, it would cause the engine to stall. Reason being, the standard pump was fitted with a hydraulic displacement control with a control range (minimum to maximum displacement) of 10 bar, whereas the OEM pump was fitted with a special control range of 35 bar. With a standard pump installed, the excavator's electronic power management system could not effectively control the pump's displacement and therefore power draw.
Obvious or not, these differences are usually enough to make it either impossible or uneconomic to adapt a unit from the component manufacturer's standard product line. Some large OEM's also manufacture their own hydraulic components. As with OEM specials, these components are a captive market for the machine dealer.
"Thanks for the great work on the two publications, Insider Secrets to Hydraulics and Preventing Hydraulic Failures. I have been in the hydraulics business for the past 20 years and it is very difficult to find any decent material on hydraulic maintenance, troubleshooting and failure analysis. These two books cover it all in easy to understand language... I conduct hydraulic training courses and plan to purchase copies to distribute to my students to share your practical approach to understanding a not so understandable subject."
Paul W. Craven, Certified Fluid Power Specialist
Motion Industries, Inc.