Basics|Precision pumping technology 3-3. Solutions to Overfeeding 2: Increase the Back Pressure

Increase the Back Pressure

The set pressure of the anti-siphon check valves used with TACMINA's compact pumps is 0.1 to 0.2 MPa. This is a fixed value and cannot be changed on site. So this is where the back pressure valve comes to play, in order to adjust the pressure.

Overfeeding can be prevented by setting the pressure of the back pressure valve to a value equal to or higher than the pressure produced by inertial resistance, which can be calculated using Equation 1 below.

(Equation 1) Pi = 2 x 10-6 x (D/d)2 x (N/60)2 x S x L x γ

Item Description Unit
Pi Pressure from the liquid's inertial force MPa
2x10-6 Conversion factor N/A
(D/d)2 Square of (Plunger diameter / Hose diameter) (cm/cm)2
(N/60)2 Square of (Strokes per minute / 60) (spm/60)2
S Stroke length cm
L Hose length cm
γ Liquid density g/cm3

For example, if the calculated value of inertial resistance is 0.3 MPa, you can prevent overfeeding by setting the back pressure valve to 0.3 MPa (at least 0.35 MPa to be sure) or a higher pressure.
However, even the adjustment of back pressure cannot raise the pressure by as much as 0.5 MPa or 0.6 MPa. In principle, the sum of the calculated inertial resistance value and the set pressure value of the back pressure valve should be 80% or below of the pump's maximum allowable pressure (catalog-listed value).

Pump's maximum allowable pressure x 0.8 ≥ Inertial resistance + Set pressure of back pressure valve

  • *
    Install the back pressure valve as close to the injection point as possible.
  • *
    Back pressure valves (anti-siphon check valves) cannot be used for any liquid containing slurry.

For example, a pump with a maximum allowable pressure of 0.5 MPa must be designed so that the sum of the inertial resistance value and the set pressure of the back pressure valve is 0.4 MPa or lower.
(In the actual pump, not all of the set pressure is applied to the pump when the back pressure valve opens, but a pressure loss occurs with the liquid passing through the valve; therefore, the calculation uses the set pressure to allow some margin of error, assuming that the whole set pressure is applied.)

TACMINA's Smoothflow Pump is a diaphragm pump with no pulsation, which relieves it from the impact of inertial resistance. Completely eliminate all overfeeding problems.
More...