MOOG D661 vs D664: Sizing for Higher Cylinder Flow

A larger cylinder or higher travel speed increases valve flow demand. Moving from D661 to D664 also affects the manifold, piping, pilot supply and control configuration.

This comparison uses the historical D660 Series Rev. H catalogue and its D661-P and D664 configurations. D661-P flow ratings here use 5 bar per metering land, separately from the 35 bar condition used for other D661 servo versions. Examples are illustrative.

Calculate the new cylinder demand

A 50 cm² effective area moving at 100 mm/s needs 30 L/min. Increasing the area to 150 cm² at the same speed raises demand to 90 L/min. Use Q = A × v × 0.006 with area in cm² and speed in mm/s.

The catalogue lists D661-P four-way grades including 30, 60 and 80 L/min at 5 bar per land, or 10 bar total across the standard four-way path. An 80 L/min grade cannot provide 90 L/min at that rated differential.

More differential may increase flow but also increases throttling loss. A pump or supply line unable to deliver 90 L/min remains a limit after fitting a larger valve.

D664 capacity is not automatically the best match

The listed D664 rating is 550 L/min, far above the example's 90 L/min demand. Assess intermediate sizes, low-opening behaviour, motion accuracy and conversion cost before selecting it.

For a 450 L/min duty, D664 becomes more relevant. However, reducing total valve drop from 10 to 5 bar gives approximately 550 × √(5/10) = 389 L/min at the same opening, below demand.

At 450 L/min and 10 bar total drop, throttling loss is about 7.5 kW. At 20 bar it is about 15 kW. Include this heat in the hydraulic-unit assessment.

Mounting and return capacity affect the conversion

The referenced D661-P four-way configurations above 60 L/min require a second return port T2. D664 uses a different mounting size, so the existing NG10 manifold is not a direct fit.

Cylinder cap and rod areas also produce different inlet and return flows in each direction. Size return passages for the actual direction and cylinder geometry.

D664 pilot configuration changes response

The catalogue lists D664-L with a single-stage ServoJet pilot and D664-P with a two-stage D630 pilot. Complete valves are respectively two-stage and three-stage designs. Listed full-stroke response times are 48 and 17 ms under the specified test conditions.

Those conditions include 210 bar pilot or operating pressure, 32 mm²/s viscosity and 40°C oil. The figures are valve response times, not complete machine cycle times.

For slow pressing, capacity and heat may dominate. Rapid reversal and tracking also require pilot transient-flow and control-bandwidth assessment.

Calculate the new demand first. Near the existing valve's capacity, investigate differential and return passages. For demands of hundreds of litres per minute, assess D664 together with its manifold, pilot configuration and throttling losses.