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Servo-Hydraulic Components Buyers Guide

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Please note that this information is intended as a guide only. Individual needs vary, for help with equipment to meet your needs, contact us. Presented with no bias.

The leading suppliers of test components are Moog, MTS, Shore Western, DTE, Team, and IST. Don't judge their products by the quality of their websites!

Actuators

All actuators sold by IST and Team use hydrostatic bearings, but the actuators from Moog, MTS, SW and DTE can be purchased with either hydrostatic or Teflon® end caps. All the actuators supplied by these vendors are fatigue rated, have an internal LVDT, and have a single piece piston rod. All except DTE and Moog are chromed. DTE uses a blue-hardening on their rods, which they claim is more durable, and Moog uses stainless-steel rods with a proprietary diamond gound coating. Given that chrome is notoriously pitted, the DTE and Moog coatings provide a better seal surface. Moog claims a 70% seal contact vs chrome, which is more like 30%. SW uses an endcap that allows quick and easy seal replacement. In fact, SW reconditions MTS actuators, and can retrofit the same endcap.

As far as performance is concerned, if you have high side-loads, then you must use hydrostatic bearings, otherwise you can save considerable money by using an actuator with Teflon bearings. When comparing apples-to-apples there is little benefit of one actuator over another, and so your decision should be based primarily on price/delivery, with the exception Moog, who have used a completely different end-cap design from the others. Their hydrostatic actuators have eight bearing pads instead of four, and they use better oil lubrication for their teflon bearings. They also claim to use a better approach for the cushions.

Most of these actuators are double-ended (equal piston area for tension and compression), but Moog, MTS, SW and DTE also have single-ended actuators available. So if you are testing a component that requires more compressive load than tensile, a spring for example, go with the single ended, it will save you more dosh. If you are in the market for a rotary actuator, your choices are limited to MTS, DTE and Team. Team has been building rotary actuators longer than anyone.

Manifolds

All these suppliers have service manifolds, known as Hydraulic Service Manifolds (HSMs) or Hydraulic Accumulation Manifolds (HAMs), and I believe they all provide for a slow ramp from low pressure to high pressure (this is typically done by porting the poppet valve pilot pressure through a reducing valve), accumulation and three micron filtration. Is any one better than another? I don't think so; all else being equal, go with the price/delivery that meets your needs.

Pumps

For quiet pumps, look at the MTS Silent Flow or Shore Western Whisper Pack. They are both quiet, using a submerged pump. There have been reports that the MTS pump suffers from insufficient circulation, causing the oil to overheat. The SW pump does not have this problem, they use an off-line "kidney loop" for cooling and filtration. Moog is working with a supplier to provide a silent pump. When the other vendors tell you they have a quiet pump, they cheat by putting their loud pump in a sound enclosure. If you are just looking for a regular, run-of-the-mill pump, you can probably do better buying one from your local hydraulics supplier. There are a few things to watch out for. If you do go that route, contact us first to ensure you have the pump adequately specified.

Swivels

MTS has the fewest options, although their 249 is the workhorse of swivels. It is durable and proven. However, its angle capability is limited in one axis, and it is very heavy. This design has been copied, and is also available from Shore Western for less. However, if you are interested in higher angles, take a look at the PK swivel from IST, and the copies of that from DTE and SW. It is a ball swivel, and has much better angle capability. SW claims that their swivel is easier to adjust, because they thread the outer ring, however the threads are not preloaded, and so I worry about fatigue failures. They use a buttress thread to minimize the problem. The other balls use set screws for preload, and they are very tough to adjust. If you want the Cadillac of swivels, take a look at Team's Hydraball. Moog has one too. They are hydrostatic ball swivels. Because they are hydrostatic, they have very low friction and hysteresis, and you never have to adjust it. I understand that they do not leak like they used to either. Make sure you get a quotation from them; they are not as expensive as you think. Also, I understand that the Hydraballs do better in an environmental chamber.

Servovalves

As far as two-stage servovalves are concerned, Moog is king. There is no other to compare. The Star valve is OK for general purpose testing, but I am not convinced they have the frequency response of the Moog. If you need any reasonable response above 100hz, then use the Team voice coil valve. The higher frequency capability comes at a price. The valve needs ultra-clean oil, and is difficult to tune. Shore Western hired a hydraulics expert who worked at MTS for many years, and developed all the baseline MTS products. He has developed a third stage valve that performs extremely well. If you need a three-stage valve, contact SW and ask them for a "Ray Lewis" valve. Don't use Atlas, they have bad spool friction and cross-over spikes.



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