Hydraulic's question

[crazyal]

This is more of a theoretical question but maybe there's reason behind it. So here's the background. Last Sunday I blew the main hydraulic hose coming off the pump on my backhoe. There's two coming out of it and I blew the 3/4" hose. The pump has a female 1" ORB output. Case installs a 1" orb to 1" 37 JIC male straight fitting. They then use a 3/4" high temp hydraulic hose with female 37 JIC fittings on each end, one straight and one 45. After that it's a 1" steel tubing. My question is why would they put the 3/4" hose? That seams like it would restrict the flow.

Because I didn't have any way of capping off the line and I wasn't sure if they were 3/4" or 1" ends on the hose I decided to buy it local. That turned into a problem because a 1" JIC to 3/4" hose 45 is not common (at least around here). I was going to use 1" all the way but the only 1" hose I could find was only rated for 2000 psi. I ended up replacing the 1" ORB to 1" JIC fitting on the pump to a 1" ORB to 3/4" JIC and the 3/4" hose. It's high pressure but not high temp (couldn't find it).

Since the hose is not very long I'm thinking about replacing it. When looking at Discounthose's website it really isn't that much more expensive to go with 1" hose over 3/4". So unless there's a reason not to then I'll probably go with 1" since there's plenty of room. Plus it's cheaper to replace the 1"ORB straight fitting to a 1"ORB 45 fitting and use straight fittings on the hose.

 

[J_J]

If the 3/4 hose can handle the flow with very little pressure losses, it should be good enough.

3/4 in hose - 18 GPM - velocity of 13.1 ft/s Recommend velocity of return hose 4-13 ft/s

1 in pressure hose - 43.2 GPM - velocity of 18 ft/s Recommend velocity of pressure hose 7-18 ft/s

If your pump flow is within this range, you should be OK

 

[MHarryE]

For a given hose type (SAE 100R1, SAE 100R2, etc.), the hose pressure rating usually drops, with hose diameter increase so it is possible they used the 3/4 inch hose to get the desired pressure capacity. Another possibility is bend radius. There are recommendations for each hose type like minimum bend radius 8 times diameter as an example so if the hose is to make a corner, they may have used the size that didn't exceed the minimum bend radius. The third option I can think of is cost. You are right in your thinking that the larger diameter hose will reduce pressure drop and will reduce heating.

 

[oldnslo]

Crazyal,
The 1" steel tubing is 1" OD and depending on wall thickness probably close to 3/4" ID so it would be about the same flow capacity as 3/4" ID hose. You may see a slightly higher pressure drop through the -16 -12 reducer fitting but I would suspect not enough to worry about.

Roy