# Articles

Articles about hydraulic, pneumatic, lube, etc. systems design.
Feel free to post your article here!

## Accumulators sizing for energy storage apps.

This week I worked on an accumulator sizing calculator for BOPs, so I have recovered my thermodynamic knowledge and just would like to note somewhere the materials summary and my thoughts about generic accumulator sizing for energy storage applications.

## Let’s get generic formula

First of all, all accumulator calculations based on a generic formula of the polytropic process (Ideal Gas Law):

##pV^{n}=const \hspace{35pt} (1)##

Where the specific value of #n# corresponds to particular cases:
#n=0# for isobaric process
#n=+\infty# for isochoric process
#n=1# for isothermal process

Now, take a look at the image and apply this formula for the accumulator’s 3 major work stages:

Sizing Accumulators

## Hydraulic manifold material selection chart

The chart of manifold’s ASSY components, provided below is not a rule or a standard, this is just what I usually use in my practice. I decided to share it because this info may be interesting for others.

Hydraulic manifold material selection chart

## Hydraulic motor case flushing

Hydraulic motor case temperature

At the latest my project I used hydraulic motor Rexroth A2FLM710 (710cc). The motor works at 1400 rpm and provides 590 HP to the consumer. For safe motor work, I always try to keep the case temperature below 80*C. The easiest way to do this is a flushing flow adjustment.

In addition to the flow, you need to keep your eyes on the motor case pressure and try balancing to prevent overpressure in the motor case (check in the motor manufacturerâ€™s catalog the max available case pressure to make longer life of motor shaft seals).

The values I have gotten: 21 GPM at 30 psi case pressure and in the worst-case scenario (max motor load, warm hydraulic oil) max case temperature was around 80*C

Hydraulic motor case flushing flow and case pressure

There are no prescriptions or recommendations for valve or orifice size in motor catalogs for flushing flow, so the selection of flushing valves is a challenge.

Of course, you can find orifices (with different diameters) provided by the manufacturer with the motor in the motor’s catalog. But the flow and result case temperature will be different from application to application and the selection of the correct orifice is an engineering responsibility without any help or advice from the motor manufacturer.

Moreover, the manufacturer can’t provide all range of orifice diameters so the selection in the catalog is usually limited. And as you can see, sometimes values of flushing flow can be really huge and the only experience helps me to select the right flushing valve size at the beginning of the project.

I still believe, manufacturers can provide some diagrams/charts with correlation “power -> flushing flow” for approximate/preliminary estimation of the flushing valve size. Because I do not think everyone has a chance to make long tests during production and play with valves sizes…

What do you think?

## Magnetic Filter Scrubber

Just impressed how efficient can be Magnetic Filter Scrubber. I use it at all applications and photos below can explain why.

Magnetic Filter Scrubber after 1 year unit work in the field

I mount these filters at the bottom of the tank downstream the butterfly shuttle valves (tank outlet ports). In case of service, these valves closing and checking/cleaning of scrubbers can be done without full oil drain from the tank. For that, each scrubber is provided with -04 orb port which lets to drain small qty of the hydraulic oil from the scrubber itself.

Magnetic Filter Scrubbers mounted to the tank

I’m not showing the brand of the scrubbers at the photo, this is not an advertisement of the specific brand, just wanna share the idea to use scrubbers, especially in the mobile applications, where the size of tanks usually not big enough to sedimentation of particles to the bottom of the tank.