Conversion from Gallons per second to Milliliters per hour

Information about the Gallon per second (gal/s)

The gallon per second is a unit of volumetric flow rate equal to one imperial gallon passing a point every second. Its symbol is gal/s. The imperial gallon is 4.54609 litres, defined in 1824 as the volume of ten pounds of water at a stated temperature, so one gallon per second moves about four and a half litres — and, conveniently, about ten pounds — every second.

Firefighting is the discipline that works at this scale. A hose reel delivers a fraction of a gallon per second, a standard hose line 1 to 2, and a major pumping appliance 10 or more. British fire service practice quoted pump capacities in gallons per minute for most of the twentieth century, and the per-second figure is what a hydraulic calculation of pressure loss in the hose actually uses.

Large pumps and water mains reach it easily. A borehole pump on a farm might deliver half a gallon per second, a district water main several tens, and a river intake for a power station hundreds. Since the gallon of water weighs ten pounds, a flow in gallons per second converts to a mass flow in stones per second by dividing by 1.4, an arithmetic that older British engineering handbooks used freely.

Flood and drainage engineering in Britain used the unit until metrication. Culvert capacities, pumping station ratings and land drainage schemes were designed in gallons per second or per minute, and much of the surviving infrastructure still carries plates giving its capacity in those terms, which anyone assessing an old asset must convert with care.

The imperial gallon must be distinguished from the American one, which is 3.78541 litres — about twenty per cent smaller. A pump rated 10 gallons per second delivers 45.5 litres per second in Britain and 37.9 in the United States, a difference far too large to ignore in any calculation of capacity or of cost.

For scale, one gallon per second fills a domestic bath in about twenty-five seconds, and 0.22 gallons per second is one litre per second. A flow of ten gallons per second is a small stream, running at about 45 litres per second.

One gallon per second equals about 4.546 litres per second, about 0.004546 cubic metres per second, or about 1.201 US gallons per second.

Information about the Milliliter per hour (mL/h)

The millilitre per hour is a unit of volumetric flow rate equal to one millilitre passing a point every hour. Its symbol is mL/h. It is the unit of slow, sustained delivery, and above all of the infusion pumps that keep hospital patients supplied with fluid, nutrition and medication over many hours.

An intravenous line is almost always programmed in millilitres per hour. Maintenance fluid for an adult runs at 80 to 125, a slow drug infusion at 5 to 20, and a paediatric or neonatal line at 1 or 2. Those are the numbers a nurse enters, and the pump converts them into the mechanical rate of a screw driving a syringe plunger.

At the bottom of that range the precision required is remarkable. A syringe driver set to one millilitre per hour is advancing the plunger by a fraction of a millimetre per minute, and it must do so smoothly enough that the drug arrives at a steady concentration rather than in pulses. The engineering of these devices is largely about eliminating the stiction that would otherwise make the delivery uneven.

Insulin pumps work below this again, in tenths of a millilitre per hour, and deliver in tiny discrete pulses rather than continuously. Implanted pumps for pain medication may run at a fraction of a millilitre per day, which is a thousandth of a millilitre per hour, and are refilled at intervals of months.

Outside medicine the unit describes laboratory perfusion, slow chemical dosing, and the leakage rates that a seal is designed to stay below. A seal specified to leak less than a millilitre per hour is losing about a cupful a week, which for many purposes is entirely acceptable and for others is a failure.

For scale, a millilitre per hour would take a full day to fill a tablespoon and about a month to fill a small cup. It is slow enough that the total delivered over a shift is the meaningful quantity, and every pump displays that alongside the rate.

One millilitre per hour equals about 0.01667 millilitres per minute, 0.000278 millilitres per second, or 0.001 litres per hour.