Hydraulic Hose theory

One thing I did not take into account early on was the compressibility of the fluid and the volumetric expansion of the hose it's self. I have seen numbers tossed around that with those two factors added togather adds up to over 40% increese in fluid in the hose. I started researching this when I came across an article saying using hoses to large can cause cylinders to become sluggish. It all comes down to fluid FPS in the hoses. Industry standard is 15-20FPS fluid velocity in hoses. Anything drastically over that number can start to cause cavitation and shorten its life. Contrary to what I always believed hose diameter does not affect flow rate just pressure.

So let's compare a 1/2" hose to a 3/4" hose connected to a 7gpm pump. A 1/2" hose would generate 11.5FPS and a 3/4" hose is 5fps. Each hose also has a pressure drop rating. 1/2" is around 10psi per 10ft and 3/4" is under 1.5psi per 10ft. So considering we are not running a lot of hose it does not affect us much. But the kicker is volumetric expansion of these hoses. Even if both hoses have the same VE factor the larger hoes will hold more fluid to the order of 2.25 times. This means the pump has to pump 2.25 times more fluid to pressurise the hose to the same pressure as a 1/2" hose. You might not think this is a big deal but it can be. Let's take say a 5ft section of both hoses. The 1/2" holds 11.8 cubic inches of fluid and the 3/4" holds 26.5 cubic inches. If we say the VE combined with fluid compressibility is 40%. At pressure it gives us an increese of 4.72 cubic inches on the 1/2" and 10.6 on the 3/4" hose. If we calculate the motor rpm and the pump output it will give us the delay from zero pressure to full pressure. My motor is 1745rpm and the pump is .92 cubic inch per revolution. With a 1/2" hose the delay is 5.13 revolutions and the 3/4" is 11.52 revolutions. Considering each revolution takes .0343839sec we get a time delay of .176sec for the 1/2" and .396 sec for the 3/4" hose.

All these numbers are really just fluff numbers to show a point that selecting the right hose is important. I don't know if the 40% is accurate or not or if it's for only one type of hose. But what it does show is the difference between these two hoses and how over sizing your hoses could end up hurting the very performance your going after. One thing larger hoses have going for them is larger fittings. Fittings have a much larger pressure drop then hose, especially 90° fittings. But you can work around this and kinda have the best of both worlds. Use reducers to and from valve assembles, pumps and cylinders. This way all your fittings can be say 3/4" which have a MUCH lower pressure drop then a 1/2" fitting. This will keep the pressure up and the smaller hose will keep the flow velocity up. It's funny becaus using larger hoses is a technique used in systems where excessive hydraulic noise is an issue or the systems need to be softened up alittle. The other great thing is smaller hoses are rated to a higher max pressure and much stiffer in responce rate. The other big advantage not normally discussed is hose bend radius. Each type and size of hose has a minimum end radius. If you exceed this minimum you compermise it's strength and life. 3/4" hose is a 4.75" minimum and 1/2" hose is 3.5" minimum. The funny thing about all this is the experts say for persized systems use 10-20fps for fluid velocity. If the pressure is constant then stay up closer to the 10fps but if the pressure is intermittent like our presses are then to stay at the upper end of max at 20fps. This means for my pump 6.95gpm and 20fps I need a 3/8" hose. Now don't that just go completely against what we have allways been told. And what's also funny is I'm running a 10hp motor so I'm putting out higher volume then most others out there that are normally around 5HP. You don't want to do the math on those pumps and the hoses thy should be running lol.

So I dont know if I'm way off in left field or not. All I know is what months of reading has shown me. So I greatly welcome any conversation on this topic here. I would be highly interested in what specs your running and how you feal it performs for you. Thanks guys for listening to my rambling like allways.

P.S. here is the chart that shows the hose size you need for your given flow rate.

So I have been doing a rather large amount of research into hydraulic systems and how to properly design them. And after all this research I have come to find out it's not as easy as I thought. First we need to narrow down what our goals are. This has also change over time from more tons to faster ram speed. So that's the direction we will look. Top Priority is ram speed and in that category I would put cylinder responce rate. By that I mean how long does it take from when I cycle the spool for the cylinder to move.One thing I did not take into account early on was the compressibility of the fluid and the volumetric expansion of the hose it's self. I have seen numbers tossed around that with those two factors added togather adds up to over 40% increese in fluid in the hose. I started researching this when I came across an article saying using hoses to large can cause cylinders to become sluggish. It all comes down to fluid FPS in the hoses. Industry standard is 15-20FPS fluid velocity in hoses. Anything drastically over that number can start to cause cavitation and shorten its life. Contrary to what I always believed hose diameter does not affect flow rate just pressure.So let's compare a 1/2" hose to a 3/4" hose connected to a 7gpm pump. A 1/2" hose would generate 11.5FPS and a 3/4" hose is 5fps. Each hose also has a pressure drop rating. 1/2" is around 10psi per 10ft and 3/4" is under 1.5psi per 10ft. So considering we are not running a lot of hose it does not affect us much. But the kicker is volumetric expansion of these hoses. Even if both hoses have the same VE factor the larger hoes will hold more fluid to the order of 2.25 times. This means the pump has to pump 2.25 times more fluid to pressurise the hose to the same pressure as a 1/2" hose. You might not think this is a big deal but it can be. Let's take say a 5ft section of both hoses. The 1/2" holds 11.8 cubic inches of fluid and the 3/4" holds 26.5 cubic inches. If we say the VE combined with fluid compressibility is 40%. At pressure it gives us an increese of 4.72 cubic inches on the 1/2" and 10.6 on the 3/4" hose. If we calculate the motor rpm and the pump output it will give us the delay from zero pressure to full pressure. My motor is 1745rpm and the pump is .92 cubic inch per revolution. With a 1/2" hose the delay is 5.13 revolutions and the 3/4" is 11.52 revolutions. Considering each revolution takes .0343839sec we get a time delay of .176sec for the 1/2" and .396 sec for the 3/4" hose.All these numbers are really just fluff numbers to show a point that selecting the right hose is important. I don't know if the 40% is accurate or not or if it's for only one type of hose. But what it does show is the difference between these two hoses and how over sizing your hoses could end up hurting the very performance your going after. One thing larger hoses have going for them is larger fittings. Fittings have a much larger pressure drop then hose, especially 90° fittings. But you can work around this and kinda have the best of both worlds. Use reducers to and from valve assembles, pumps and cylinders. This way all your fittings can be say 3/4" which have a MUCH lower pressure drop then a 1/2" fitting. This will keep the pressure up and the smaller hose will keep the flow velocity up. It's funny becaus using larger hoses is a technique used in systems where excessive hydraulic noise is an issue or the systems need to be softened up alittle. The other great thing is smaller hoses are rated to a higher max pressure and much stiffer in responce rate. The other big advantage not normally discussed is hose bend radius. Each type and size of hose has a minimum end radius. If you exceed this minimum you compermise it's strength and life. 3/4" hose is a 4.75" minimum and 1/2" hose is 3.5" minimum. The funny thing about all this is the experts say for persized systems use 10-20fps for fluid velocity. If the pressure is constant then stay up closer to the 10fps but if the pressure is intermittent like our presses are then to stay at the upper end of max at 20fps. This means for my pump 6.95gpm and 20fps I need a 3/8" hose. Now don't that just go completely against what we have allways been told. And what's also funny is I'm running a 10hp motor so I'm putting out higher volume then most others out there that are normally around 5HP. You don't want to do the math on those pumps and the hoses thy should be running lol.So I dont know if I'm way off in left field or not. All I know is what months of reading has shown me. So I greatly welcome any conversation on this topic here. I would be highly interested in what specs your running and how you feal it performs for you. Thanks guys for listening to my rambling like allways.P.S. here is the chart that shows the hose size you need for your given flow rate.