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Examples of How to Calculate Flow Resistance for Liquids

Problem 1. A restrictor is required to flow 0.1 GPM of 50/50 ethylene glycol/water blend (specific gravity = 1.07) at 45°F and 6 psid. How many Lohms are required?

Solution:

  1. Read kinematic viscosity; v = 5.0 cs from curve on pages S53-54.
  2. Use v and ΔP to determine viscosity correction factor, V = .87, from curve on page S7.
  3. Select unit constant K from table on page S6.
  4. Compute Lohms required.

 


Problem 2. What pressure drop will result from a flow of 57 mL/min. of 50/50 ethylene glycol/water mixture (specific gravity = 1.07) at 45°F, flowing through a 1000 Lohm restrictor?

Solution:

  1. Find viscosity from pages S53-54. v = 5 cs
  2. Use knowledge of system to assume initial solution.
    H = 4 psid
  3. Use assumed H to determine V = 0.75 from table on page S7.
  4. Select units constant K from table on page S6.
  5. Compute trial ΔP
  6. Make trials as required to find correct solution.
    H = 2 psid     V = .55

Problem 3. What restriction will permit a flow of 1 gallon of water per hour at 50 psi ΔP?


Problem 4. A jet with a hole diameter of .012" flows 18 lb/hr of water at 100 psi ΔP. How many Lohms?


Problem 5. What ΔP will be required to flow 20 GPH of water through a 2000 Lohm Jet?


Problem 6. What water flow will result from a restriction of 500 Lohms and a ΔP of 500 psi?

Note: For special flow requirements, The Lee Company can determine the required Lohm rating.


Problem 7. A restrictor is required to flow 0.15 GPM of MIL-H-83282 hydraulic fluid at 80°F and 100 psi ΔP. What restriction is required?

Solution:

  1. Read specific gravity; S = 0.84 from chart on page M17.
  2. Read viscosity; v = 21cs. From chart on page M14.
  3. Use viscosity and ΔP to determine viscosity compensation factor V = 0.95 from graph on page M13.
  4. Select units constant, K = 20 from table on page M10.

Problem 8. What pressure drop will result from a flow of 5 PPH of SAE #10 lubricating oil at 20°F, flowing through a 1000 Lohm restrictor?

Solution:

  1. Read specific gravity and viscosity.
    S = 0.90, v = 600cs.
  2. Use knowledge of system to assume solution.
    H = 50 psid.
  3. Use assumed ΔP to determine V = 0.18
  4. Select units constant, K = 10,000 from table on page M10
  5. Compute trial ΔP.
  6. Make trials as required to find correct solution.
    H = 26 psid.

Problem 9. A Safety Screen is required to flow 775 lb/hr of JP4 @ 80°F with a maximum pressure drop of 5 psid. What is the maximum Lohm rate allowed for the Safety Screen?

Solution:

  1. Find specific gravity; S = 0.77 from curve on page M16.
  2. Find viscosity; v = 1cs from curve on page M14.
  3. Use v and ΔP to determine viscosity compensation factor, V = 1.0 from curve on page M13.
  4. Select units constant, K = 10,000 from table on page M10.