Get What You Spec’d

•  Do not allow the use of suction strainers: I continually see suction strainers creating more problems than they solve. Because they are typically supplied with no way to monitor vacuum, if they become clogged, they eventually cavitate the pump causing it to fail. If you still feel compelled then specify the strainer with an electrical vacuum switch that shuts the pump off if vacuum at the inlet to the pump gets too high. This will save the pump from damage.

•  No pipe thread ports or fittings: Pipe thread is a dinosaur in hydraulics because it leaks and contaminates. Acceptable fittings are anything that seal with an o-ring along with flared and flareless tube fittings.

Performance specs
As far as operating costs are concerned, there are several factors that will influence the lifecycle costs of a new system such as input power requirements and circuit efficiency. Remember, the cheapest option up front is not always the cheapest to operate. The specification should clearly define some key requirements such as:

•  Request system efficiency calculations: Although the capital cost of a more efficient system may be higher, the energy savings will pay for the up front cost in short order if the system is well designed. This calculation will include losses from the pump and motor as well as throttling, valve and line losses. Assuming a power cost of $0.10/kw-h expect costs of $38 per year for 24/7 operation for every 1 USgpm pushed against 100 psi.

If you have a system where 40 gpm is pushed through lines/valves with 100 psi resistance, the cost is $1,525/year in wasted energy. You then also have to pay to remove this heat to boot. In this example, spending a bit extra on larger lines may yield significant returns for the life of the systems.

•  Cooler capacity based on circuit efficiency: System efficiency numbers will determine how much cooler capacity is required. Allow at least 50% extra capacity so the cooler can keep up under the worst conditions (i.e. increased component internal leakage due to wear). The system may need to run at decreased efficiency until the problem is found and fixed.

It’s clear that the tighter the specification the more likely you are to get what you paid for. A little bit of work up front nailing down what you want will pay off. The only thing left to do is put that savings to work.
www.cfp.ns.ca

Pat Jones, P.Eng, is the owner of Consolidated Fluid Power (CFD) Ltd., where he is an instructor and consultant with more than 20 years of hands-on experience in the fluid  power industry.