The Smart Manifold
by Jon Wilcox

Every manifold that can be invented has been invented. WRONG! Hydraulics is known to be a mature industry. However, innovation is still being accomplished. Hydraulic circuits for new manifolds are invented every day.

Manifold materials and machining techniques are still evolving. The industry is pressing towards higher pressure, greater reliability, decreased likelihood of leaks, lighter materials, and better design methods. Kinetics Ltd. has been in the defense and aerospace manifold business for 30 years and a lot has progressed in that time.

Key to successful manifold design starts with the circuit. Attention must be given to the application. If the application is not well understood, the circuit may be done in a more complicated way than necessary or it may just plain not work. Every military program or process deserves a good acronym. I feel that “TSTBALAIW” (pronounced testballaywa) is a good corollary to the KISS (keep it simple stupid) acronym. It means the simpler the better as long as it works. We must account for all realistic scenarios and ensure that the circuit works for each one. This starts with understanding the motion control. What are we trying to move? How much force is necessary? How long should it take to get there? Does the load change with position? Does the load go over center (from push to pull or vice versa)? Are multiple functions performed at the same time? Are the functions open or closed loop? What power is available for control? Are valves actuated mechanically, hydraulically, pneumatically, or electrically? These are some of the basic questions that must be asked.

Smart companies ask the experts in the industry how best to do things. They are the ones that aren’t affected by the NIH syndrome (not invented here). They start with the basics, what motion they want accomplished. They don’t tell you how it should be accomplished. They write a performance specification on the system, not the component. Suppliers can then quote a whole system and describe their advantages. It may be that some vendors know the potential pitfalls and work their way around them. By comparing bidder’s responses, you can get a good idea of who the smart ones are and proceed forward with the top one or two to obtain prototypes. Ideally, each vendor should spend time with the customer prior to the actual quoting phase. You will likely get better and quicker proposals back that way. The only concern is that proprietary information should remain that way and not go back into the vendor specification.

Great companies figure out how to evaluate a project before the proposals are sent back from the suppliers. They figure out what is most important to them. For defense applications, given the starting point meets the basic motion control performance, evaluation criteria should fall into the following categories:

Initial System Price (Manifold price may be higher than others but could save significant dollars on other components and system assembly and test times)

Ø Life Cycle Cost
Ø Weight
Ø Compact size / fit into the vehicle
Ø Reliability
Ø Serviceability / Troubleshooting Ease

Evaluation criteria weights should be given for each of the categories totaling 100%. Points should be given for meeting each criteria. Multiplying the category points times the % and summing the total points should point to the winner. This helps to make a more un-biased decision that will benefit the company

Basic performance criteria for the system must be spelled out in detail. These are the areas that are “must meet performance”. If the supplier can’t meet these areas, then there is no need to evaluate the points. Performance requirements fall into the following categories:

1. Motion control – time vs. position (acceleration & velocity)
2. Motion control – force vs. position
3. Allowable fluids
4. Ambient temperature range
5. Maximum size of actuators
6. Available space claim for components (i.e. diameter & length of linear actuators and motors; length, width & height of pump, reservoir & manifolds.

Once the system parameters are established, the manifold design is of great importance. This is where plumbing can be reduced to the bare minimum which means greater reliability and less potential for leakage. The circuit can be established which then defines the bill of material and subsequently how the manifold can be designed. It then becomes the skill of the design engineer how to package the valves in the tightest package without sacrificing the integrity of the manifold. To further complicate things, the system designer often will establish preferences for location of the ports since that will tend to minimize hydraulic lines from crossing over each other and minimize the hydraulic line lengths. This further establishes the importance of knowing what the system must accomplish. Obviously, the designer must be aware of minimum wall thicknesses for the selected manifold material. Both tensile strength and low cycle fatigue must be taken into consideration for these wall thicknesses as well as stress raisers.

In summary, smart companies work with smart suppliers to make smart manifolds. Creative ideas that save the company time, money, and weight are generated by innovative companies responding to well thought out system requirements. To that end, let the creative juices flow and your company succeed.