## Charge pump displacement

There is a generic rule for close loop systems, to select the charge pump size: pump displacement should be at least 10% of the combined displacement of the pump and motor. To understand where this value comes from let’s figure-out all factors in the system what influence on a charge flow:

1. The charge pump has to supply enough flow to compensate for leaks due to the volumetric efficiency of the pump and motor. This is why sometimes the charge pump called a “replenishing pump”.

In general, volumetric efficiency of pump and motor in the hydrostatic transmission is around 96..97%, so system overall volumetric efficiency is around 93%. It means 7% of the theoretical pump flow is the leaks which need to be somehow compensated.

2. Addition flow needs for flushing of both main pump case and motor case to remove the hottest oil from the system.

Adding a hot oil shuttle valve at the motor removes the hottest oil in the loop through the motor case drain. Normal practice is to run the motor case back to the bottom drain port of the main pump then from the top pump’s drain port to the cooler (see the picture above).

There no ways to calculate exactly the required flushing flow through the motor. You need some experience with different applications and motor sizes, you have to do tests and check recommendations from the motor manufacturer. The generic rule to find the best flushing flow rate: motor should not be overheated in the worst-case mode.

3. Charge pump itself has huge internal leaks.

Mostly charge pump is a vane or gear type, and the volumetric efficiency of these type of pumps is very low, around 80%.

4. A small qty of flow is required to power the pump’s control system.

This qty of flow is pretty small.

Of course, different systems require different approaches to the calculation of charge pump displacement. And sometimes we have to make some compromises. If you have doubts – just ask a question!

## SUN Hydraulics – delivery time issue

Working on the design of new projects I like to involve SUN Hydraulics valves and use them a lot. They are not expensive, pretty reliable and have uncredible understandable paper and online catalogs.

All these major benefits coming to naught as soon delivery time even of very wonderfull products makes impossible to use them in projects. This is exactly what going on these days.

Today I got a quotation from a local vendor for the valve FDEA-LAN with delivery time 31 weeks!!! It is longer than my project needs to be completed!

Helios Technologies (formerly known as Sun Hydraulics) has three facilities in the Americas, two in Europe and already three in Asia-Pacific (one more plant in China has been opened this year). But this fact doesn’t help to provide SUN valves faster.

Because the company, where I’m working now, has fillies in Europe we know the issue with the SUN product delivery time is currently common for the whole world. There no any comments from SUN and its parent Helios at their websites and I see the delivery time is increasing every month.

Therefore, I’m seriously starting to think about solutions on how to proceed. Problem is a lot of manifolds that have already been designed in our projects use SUN cavities. And to re-design of these manifolds is a pain, you know why. I’m seriously thinking to use SUN clones to cover these positions. Currently, I dug the next manufacturers:

• Winner Hydraulic. This is a manufacturer from Taiwan, but they do not have distributors in North America.
• PressureBoss Hydraulics Inc. From their website is not clear what country their plant is physically situated. They have distributors in the US but not in Canada.

For new projects, I’m starting to look at Parker and Eaton cartridges. They have a pretty good assortment and actually last months I already used some of their valves as quick replacement options.

How you are dealing with SUN Hydraulic delivery issue?

## Mounting flanges and shafts of pumps and motors

Just to determine what flange and shaft of pump or motor you have, please see below excerpts from the next standards:
SAE J744. “Hydraulic Pump and Motor Mounting and Drive Dimensions”.
ISO 3019-1. “Dimensions and identification code for mounting flanges and shaft ends of displacement pumps and motors”.

### Two bolts mounting flange

Two bolts mounting

## Temperature-Viscosity Chart

The interpolation calculator provided below is used to determine:

• the kinematic viscosity values, depends from temperature, calculated by the formulas specified in ASTM D341 – (‘Standard Practice for Viscosity-Temperature Charts for Liquid Petroleum Products’);
• the Viscosity Index (VI) by the formulas specified in ASTM D2270 (Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 and 100°C 1) or in ISO 2909 (Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 and 100°C 1) or in ГОСТ 25371-2018 (Нефтепродукты. Расчёт индекса вязкости по кинематической вязкости)

#### Annotation.

Any mineral oil is supplied with the specification of kinematic viscosity values at two different temperatures, usually at 40°C and at 100°C (or at 100°F and at 210°F). These data is enough to determine kinematic viscosity at any other values of temperature and as well Viscosity Index.

You can calculate pre-filled values of oil classified by ISO 3448 with grades VG22, VG32, VG46 or VG68 (at viscosity Index = 100) or enter specific values for any other oils.