Basics｜Precision pumping technology 3-2. Solutions to Overfeeding 1: Reducing the Inertial Resistance

Reducing the Inertial Resistance

The inertial force (inertial resistance) in a metered pump can be expressed by the following equation:

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

Let's break down this equation and look at the individual factors.
The factors will be as follows for plunger pumps. In the case of standard diaphragm pumps, the effective diaphragm diameter is used instead of the plunger diameter (D) below. The rest is exactly the same.

Item Description Unit
Pi Pressure from the liquid's inertial force MPa
2 x 10-6 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
  • Proportional: a) stroke length, b) hose length, c) liquid density
  • Proportional to the square: d) plunger diameter, e) strokes per minute
  • Inversely proportional to the square: f) Hose diameter

Next, let's look at the meaning and its impact for each item.

Elements That Affect the Inertial Resistance and the Degree of Their Impact (1)

Symbol a: Stroke length

Impact How to reduce inertial resistance Advantages and disadvantages

Proportional

(Example)
Reduce stroke length by half ↓
Inertial resistance reduced to half ↓
However, discharge volume is also reduced to half

Shorten the stroke length
(Adjust with dial)
  • Advantage(s)
    • Easy operation
  • Disadvantage(s)
    • Chemical needs higher concentration due to the reduced discharge volume
    • If undiluted chemical is needed, concentration cannot be increased
    • Corrosion resistance must be reviewed again for higher-concentrated chemical
    • Liquid density increases with higher concentration, which may balance out the effect of reduced stroke length

Symbol b: Hose length

Impact How to reduce inertial resistance Advantages and disadvantages

Proportional

(Example)
Reduce hose length by half ↓
Inertial resistance reduced to half

Shorten the hose
  • Advantage(s)
    • Simply cut the hose
  • Disadvantage(s)
    • Tank and pump installation locations need to be changed
    • Moving only the pump makes the hose at the suction side longer (in principle, the suction-side hose is better as short as possible)

Symbol c: Liquid density

Impact How to reduce inertial resistance Advantages and disadvantages

Proportional

(Example)
Reduce liquid density by 20% ↓
Inertial resistance reduced by 20%

Dilute the chemical
However, not to a significant extent
  • Advantage(s)
    • Simply thin the chemical with water (solution)
  • Disadvantage(s)
    • Pump and tank may not have sufficient capacity due to the reduced density

Elements That Affect the Inertial Resistance and the Degree of Their Impact (2)

Symbol d: Plunger diameter

Impact How to reduce inertial resistance Advantages and disadvantages

Proportional to the square

(Example)
Reduce the plunger diameter by half ↓
Inertial resistance reduced to 1/4 ↓
However, discharge volume is also reduced to 1/4

Changing the plunger diameter is not practical
  • Disadvantage(s)
    • Smaller plunger diameter significantly decreases the discharge volume

Symbol e: Stroke speed

Impact How to reduce inertial resistance Advantages and disadvantages

Proportional to the square

(Example)
Reduce stroke speed by 50% ↓
Inertial resistance reduced to 1/4 ↓
However, discharge volume is reduced to half

Control the rotation speed using an inverter, etc.
  • Disadvantage(s)
    • Needs an inverter or other mechanism
    • Not to the same extent as reducing the plunger diameter, but the same disadvantages as "a" exists, deriving from the reduced discharge volume

Symbol f: Inner diameter of hose

Impact How to reduce inertial resistance Advantages and disadvantages

Inversely proportional to the square

(Example)
Double the inner diameter of the hose ↓
Inertial resistance reduced to 1/4 ↓
No change in discharge volume

Increase the hose diameter
  • Advantage(s)
    • No need to change the installation conditions
    • Significant reduction of inertial resistance can be expected
    • Construction work costs are relatively low
  • Disadvantage(s)
    • More liquid accumulates inside the hose due to the increased hose thickness
    • Hose couplings may need to be changed

onsidering the above chart, the most effective way is "f."
Replacing the hose with a thicker one is relatively easy to do; additionally, the effect is squared in value without the need to consider any changes in the discharge volume. However, to prepare for the disadvantages, it is still important to consider the pump layout and the inertial resistance before installing the metered pump.

TACMINA's Smoothflow Pump is a diaphragm pump with no pulsation, which relieves it from the impact of inertial resistance. Saves you costs by supporting narrower and longer pipes.
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