Non-Compensated Flow Control Valve
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| Illustration 1 | g01064421 |
The schematic that is shown in Illustration 1 consists of the following components:a positive displacement pump, relief valve, cylinder, non-compensated flow control valve, two pressure gauges and a three-position, four-way, tandem-centered, lever operated directional control valve.
The non-compensated flow control valve consists of a variable orifice and a check valve. When oil flows into the cylinder head end, the check valve seats. The variable orifice controls oil flow into the head end. When oil flows out of the cylinder head end the check valve opens. The oil follows the path of least resistance. The oil flows through the check valve without any restrictions.
In a non-compensated flow control circuit, any change in the pressure differential across the orifice will produce a corresponding change in the flow through the orifice.
The relief valve is set at 3445 kPa (500 psi). The orifice is adjusted to a flow of 18.9 L/min (5 US gpm) at 3445 kPa (500 psi) with no load on the cylinder. The pressure differential across the orifice is 3445 kPa (500 psi). Total pump oil flows through the orifice to the cylinder.
Load Increase
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| Illustration 2 | g01064424 |
Illustration 2 shows that the cylinder load is increased. The cylinder pressure that is required to overcome the resistance of the load is 1378 kPa (200 psi). The 1378 kPa (200 psi) is subtracted from the available 3445 kPa (500 psi) upstream of the orifice. This reduces the pressure differential across the orifice to 2067 kPa (300 psi). The 2067 kPa (300 psi) causes the flow through the orifice to decrease to 11.4 L/min (3 US gpm). Any attempt to increase the flow through the orifice will cause the system pressure to increase above the relief valve maximum setting of 3445 kPa (500 psi). The remaining 7.6 L/min (2 US gpm) causes the system pressure to increase above 3445 kPa (500 psi). The relief valve opens and 7.6 L/min (2.0077 US gpm) flows across the relief valve to the tank.
A decrease in the flow through the orifice causes a corresponding decrease in the speed of the cylinder.
Load Decrease
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| Illustration 3 | g01064425 |
Illustration 3 shows the cylinder load that is decreased. The pressure that is required to overcome the resistance of the load decreases to 689 kPa (100 psi). The 689 kPa (100 psi) is subtracted from the available 3445 kPa (500 psi) upstream of the orifice. The new pressure differential across the orifice is 2756 kPa (400 psi). The 2756 kPa (400 psi) causes the flow through the orifice to increase to 15.1 L/min (4 US gpm). Any attempt to increase the flow through the orifice above 15.1 L/min (4 US gpm) will cause the system pressure to increase above the relief valve maximum setting of 3445 kPa (500 psi). The remaining 3.8 L/min (1 US gpm) causes the system pressure to increase above 3445 kPa (500 psi). The relief valve opens and 3.8 L/min (1 US gpm) flows across the relief valve to the tank.
An increase in the flow causes a corresponding increase in the speed of the cylinder.
In Illustration 2 and 3, increasing the relief valve pressure setting to 4823 kPa (700 psi) allows the pump to send the maximum flow of 18.9 L/min (5 US gpm) through the orifice, as long as the cylinder load pressure is less than 1378 kPa (200 psi). The pressure differential across the orifice will always be greater than 3445 kPa (500 psi) and flow through the orifice is limited by the output of the pump. Therefore, the speed of the cylinder will remain constant as the pressure changes between 1378 kPa (200 psi) and 689 kPa (100 psi).