Page 4 - Parker - Load and Motor Control Valves

Catalog HY15-3502/US
Technical Tips Load and Motor Control Valves

CV
Selection Options (Continued) Thermal Setting – Counterbalance valves have a
built-in thermal relief valve that compensates for the
Pilot Ratio – The pilot ratio is the ratio of the pilot area
expansion of oil, due to temperature, by bleeding off
versus the differential area poppet. Thus, the higher
Valves
excess pressure. In other words, the thermal setting is
Check
SH the pilot ratio, the less pressure that is needed to the pressure that the counterbalance will unload at if
assist the load pressure in unseating the poppet. This
no pressure is present at the pilot port. Obviously, this
means there is less restriction to the overrunning load,
setting should be above the holding setting. The Parker
resulting in less horsepower required and more control
MHC counterbalance valves are automatically set
of the load. So higher pilot ratio equates to less
Valves
Shuttle
LM 1000 psi above the holding setting of the valve. You do
restriction to the overrunning load, less control and
not specify this setting, only the holding setting.
less horsepower required. Lower ratio equates to more
For the CB101 Series, you do specify the Thermal/
restriction to the overrunning load, more control and
Crack setting in the model code. The holding setting
more horse- Pilot Ratio
Controls
Load/Motor
FC power required. (maximum load induced pressure) is 70% of that
The pilot ratio 10:1 specified setting. Example: Hold at 3000 psi, crack at
decision is one 6:1 Control HP Required 4285 psi. For the E2 Series, you specify the Thermal/
of Horsepower Crack setting in the model code. The crack setting
4:1 (maximum load induced pressure) should be 1.3 times
Controls
Flow
versus Control. For
PC 1:1 the hold. Example: Hold at 3000 psi, crack at 3900 psi.
reference the most
popular ratio is 6:1. Pilot Area – The pilot pressure required to lower the
Less More
cylinder when fully loaded and unloaded can also be
determined before applying the valve. The pilot pres-
Pressure
Controls
LE Sample Ratios: sure can be determined by the below equation:
10:1
Primary function is load holding or hose break P = (T – L) / R
protection P S P
Loads moving at fast speeds and positioning is P = Pilot Pressure
Elements
Logic
P
DC not critical T = Thermal Setting
S
7:1, 6:1 and 5:1 L = Induced Load
Most popular starting ratio R = Pilot Ratio
4:1 and 3:1 P
Positioning is critical such as a pick and place Example:
Controls
Directional
MV application
Instability with 6:1 ratio The maximum load is 3000 psi. A 6:1 Pilot Ratio was
chosen and the thermal relief setting is the standard
1:1
Motor control application 1000 psi over load setting. What is the pilot pressure
required to retract the cylinder if it is fully loaded? What
Manual
Valves
SV ADJUSTMENT TYPE pilot pressure is required to retract the cylinder if there
is no load?
Parker offers counterbalance valves with adjustable LOAD NO LOAD
and non-adjustable pressure settings. The non-
adjustable or shimmed version is recommended for
Valves
Solenoid
PV
most applications as it prevents tampering or improper
adjustment by uneducated end users.
FULLY LOADED:
SELECTING SETTINGS
Proportional
Valves
P = (4000 psi – 3000 psi) / 6
P
CE There are three basic settings to consider before P = 1000 psi / 6
finalizing a counterbalance valve for your application. P
P = 167 psi
P
Holding Setting – The holding setting is sometimes
Thus, any time the pilot line sees at least 167 psi, the
referred to as the counterbalance setting. It is the
Electronics
Coils &
cylinder could lower the load.
BC maximum load setting you expect the counterbalance
to hold. Note that the counterbalance valve should be UNLOADED:
set for the absolute maximum hold pressure required.
P = (4000 psi – 0 psi) / 6
Also note that counterbalance valves are restrictive P
P = 4000 psi / 6
Cavities
Bodies &
type devices and as such are not ideal for low pres- P
TD P = 667 psi
sure applications, such as those below 750 psi. The P
holding setting is the setting you choose when select- Thus, at least 667 psi will be needed to lower the
ing a counterbalance valve. cylinder when it is unloaded.
Technical
Data
LM3 Parker Hannifin Corporation
Hydraulic Cartridge Systems