Question: What is the lowest temperature we can safely operate our Darley pump?
This question is asked by many pump operators in the upper Midwest of the United States and Canada during the winter season.
Wayne Hable, P.E. Chief Engineer.
Answer. Thinking the elastomer components in the pump are the limiting factor here, their temperature ranges are as follows:
The majority of mechanical seals are good to a temperature range of -40°F (-40°C) to 180°F (82°C). The H100 mechanical seal (2nd stage pump) is good to a temperature range of -20°F (-29°C) to 275°F (135°C). The buna O-rings, which we typically use for sealing the pump, are good to a temperature range of -22°F (-30°C) to 212°F (100°C). The Viton O-rings, which we typically use for sealing the transmission, are good to a temperature range of -65°F (-55°C) to 390°F (200°C). The rubber lip oil seals that we use are good to a temperature range of -40°F (-40°C) to 250°F (121°C).
The 80W-90 oil is the next item to consider. Petroleum based 80w-90 oil has a pour point of -25°F (-33°C). Synthetic based 80w-90 oil has a pour point of -44°F (-42°C). Pour point of an oil is where it becomes a solid so to speak. You don’t want to take the pump transmission down in temperature until it’s at its oil pour point temperature – the oil then behaves like a solid at its pour point and that may cause issues trying to conjugate the oil thru the gear mesh and rolling bearings. I think a 4F to 5F safety factor between the oil pour point and its safe operating point would be wise to consider. Therefore, I’d say petroleum based 80W 90 should be good down to a -20°F (-29°C) temperature and synthetic based 80W-90 oil should be good down to a -40°F (-40°C) temperature.
All of these factors add up to imply that buna O-rings would be the limiting factor at -22°F (-30°C) for low temperature applications if synthetic based 80W-90 oil was used on a non 2nd stage pump. Therefore, -20°F (-29°C) would be the limiting factor if petroleum based 80W-90 oil was used. If we switched all the O-rings to Viton and used synthetic based 80W-90 oil, then the lowest temperature we could possibly go down to would be -40°F (-40°C) on a non 2nd stage pump.
This is with the understanding the pump is kept drained of water 80W-90 oil has a pour point of -25°F (-33°C). Synthetic based 80W-90 oil has a pour point of -44°F (-42°C). Pour point of an oil is where it becomes a solid so to speak. You don’t want to take the pump transmission down in temperature until it’s at its oil pour point temperature – the oil then behaves like a solid at its pour point and that may cause issues trying to conjugate the oil and dry when at or below 32°F (0°C). Overall, these temperature considerations highlight the importance of selecting the correct elastomers and lubricants for the expected operating environment. Ensuring the appropriate combination of O-rings, seal materials, and oil type will help maintain pump reliability and prevent cold-temperature performance issues.
