MTS Series 685 Hydraulic Grip Supply - Manual (Page 35)

Determining the Grip Operating Pressure
Series 685 Grip Supply Product Information Operation 35
Determining the Grip Operating Pressure
You must consider the following factors to determine the appropriate grip
operating pressure:
• The type of grips to be used
• The specimens to be tested
• The tests to be performed
• The model number of the grip supply
Grip manuals (from MTS) describe how to determine the required operating
pressure. They include formulas or graphs to determine the grip pressure (also
called minimum operating pressure). The minimum pressure, as referred to in the
grip manual, is the calculated least pressure that will provide adequate gripping
of the specimen while it is being tested at specific maximum loads.
If practice indicates that the calculated pressure proves to be too low (because the
specimen slips under load due to hardness or other characteristics), then the
actual minimum pressure will have to be increased to provide adequate gripping.
Use the grip manual to determine the minimum grip operating pressure that is
best for the test situation at hand.
The grip supply can be configured to produce different output pressures. Check
the model number specification. See “Adjusting the Output Pressure” for the
procedure.
How to Adjusting the Output Pressure
The output pressure of the hydraulic grip supply determines the gripping force
applied to the specimen by the grips. The output pressure can be adjusted up to
3 Pressure control Adjusts the amount of hydraulic pressure applied to the grips to grip the
specimen. There is a valve for the upper grip and another valve for the lower
grip.
These are multi-turn valves. Pressure increases as the knob is turned clockwise
and decreases as the knob is turned counterclockwise. The adjustment range
depends on the model number of the hydraulic grip supply.
To determine the correct operating pressure, see “Adjusting the Output
Pressure.”
4 Grip Controls Controls are provided for the upper grip and lower grip for specimen
installation and removal. The three-position controls can grip or release one
end of a specimen.
Indicators are provided to show the grip control position. Turn the control
clockwise to clamp a specimen into the grip. Turn the control
counterclockwise to release a specimen from the upper grip. The gripping
action can be stopped at a detent between grip and ungrip by moving the
control midway between the two grip symbols.
I TEM C ONTROL D ESCRIPTION