System Design Parameters; Filtration System; Reservoir - Danfoss H1 Series Technical Information

Technical Information
H1 Bent Axis Variable Displacement Motors, Size 060/080/110/160/210/250

System design parameters

Filtration system

Reservoir

28 | © Danfoss | December 2016
To prevent premature wear, ensure that only clean fluid enters the hydrostatic transmission circuit. A
filter capable of controlling the fluid cleanliness to ISO 4406, class 22/18/13 (SAE J1165) or better, under
normal operating conditions, is recommended.These cleanliness levels cannot be applied for hydraulic
fluid residing in the component housing/case or any other cavity upon delivery from the factory.
The filter may be located on the pump (integral) or in another location (remote or suction). The integral
filter has a filter bypass sensor to signal the machine operator when the filter requires changing. Filtration
strategies include suction or pressure filtration. The selection of the filter strategy depends on a number
of factors including the contaminant ingression rate, the generation of contaminants in the system, the
required fluid cleanliness, and the desired maintenance interval. Filters are selected to meet the above
requirements using rating parameters of efficiency and capacity.
Filter efficiency can be measured with a Beta ratio (β
transmissions and open circuit transmissions with return line filtration, a filter with a β-ratio within the
range of β = 75 (β ≥ 2) or better has been found to be satisfactory. For some open circuit systems,
35-45 10
and closed circuits with cylinders being supplied from the same reservoir, a higher filter efficiency is
recommended. This also applies to systems with gears or clutches using a common reservoir. For these
systems, a charge pressure or return filtration system with a filter β-ratio in the range of β
10) or better is typically required.
Because each system is unique, only a thorough testing and evaluation program can fully validate the
filtration system. For more information, see Design Guidelines for Hydraulic Fluid Cleanliness, Technical
Information BC00000095.
Filter β -ratio is a measure of filter efficiency defined by ISO 4572. It is defined as the ratio of the number
x
of particles greater than a given diameter ("x" in microns) upstream of the filter to the number of these
particles downstream of the filter.
Filtration, cleanliness level and β
Cleanliness per ISO 4406
Efficiency β (charge pressure filtration)
x
Efficiency β (suction and return line filtration)
x
Recommended inlet screen mesh size
Proper sizing of the hydrostatic system reservoir will allow maximum volume changes during all system
operating modes and increase de-aeration of the fluid as it passes through the tank. A suggested
minimum total reservoir volume is
fluid volume equal to ½ of the maximum charge pump flow per minute. This allows 30 seconds of fluid
dwell time for removing entrained air at the maximum return flow. This is usually adequate to allow for a
closed reservoir having no breather in most applications.
Locate the reservoir outlet to the charge pump inlet above the bottom of the reservoir to take advantage
of gravity separation and prevent large foreign particles from entering the charge inlet line. A 100-125
mesh screen over the reservoir outlet port is recommended. Position the reservoir inlet for the fluid
return to discharge below the normal fluid level and toward the interior of the tank. A baffle or baffles,
between the inlet and outlet of the reservoir will further increase de-aeration and reduce surging of the
fluid.
). For simple suction-filtered closed circuit
X
-ratio (recommended minimum)
x
22/18/13
β = 75 (β
15-20
β = 75 (β
35-45
100 – 125 µm
5
∕ of the maximum charge pump flow per minute with a minimum
8
= 75 (β
15-20
≥ 10)
10
≥ 2)
10
11037153 | BC00000043en-US1103
≥
10