PHILADELPHIA — For more than 100 years, the cloistered nuns known as the Pink Sisters have worked in shifts to ensure nonstop prayer in Philadelphia’s Chapel of Divine Love.

Now, to address their shrinking numbers and ensure their prayers continue for another century, the Roman Catholic Holy Spirit Adoration sisters have begun quietly reaching out, seeking to grow their order while carefully maintaining their secluded life.

In the last year, they hung a banner outside their chapel and convent as a way to let other people know about their daily public Masses. They’ve granted more interviews with news reporters. And they have begun inviting Catholic women’s organizations and schools to speak to the sisters — with all conversations taking place through the grille in the convent visiting room, of course.

There’s even a subtle recruitment flier hanging just inside the front door of the chapel. It encourages visitors to ask themselves three questions: Do you love Jesus in the Blessed Sacrament? Do you realize the power of prayer before the Blessed Sacrament? Is Jesus calling you to say “yes” to a life of prayer before the Blessed Sacrament?

“We rarely reached out for vocation promotion before the centennial. But now we want young ladies to see how beautiful the life is and how truer the joy when it is without the trappings of material things,” said Sister Maria Clarissa, 55. “We do our part in addressing these challenges, but at the same time, we leave it to the Lord. He’s the one who calls.”

There were once as many as 40 nuns living in the Philadelphia convent. Now there are 20: The youngest is 52, and the oldest is 90.

The order was founded in Holland in 1896 with a focus on the perpetual adoration of the Blessed Sacrament, the consecrated bread they uphold as the body and blood of Christ. The rose-hued habits are meant to symbolize the joy the sisters feel honoring the Holy Spirit.

In 1915, nine of the original sisters left the motherhouse and came to Philadelphia, where they were invited to open the order’s second convent.

Today there are about 420 Holy Spirit Adoration sisters living in 22 convents in 12 countries. There are three other US convents — in St. Louis; Corpus Christi, Texas; and Lincoln, Nebraska.

It may come as a surprise to some that a group of 20 nuns live a contemplative, secluded life not far from Philadelphia’s famed museums, historic landmarks and government. The sisters leave the cloister only for emergencies, such as medical appointments. When they do venture out, the sisters wear gray so as not to draw too much attention to themselves.

It is a selfless life, focused on offering intercessory prayers on behalf of people they will never meet living in places they will never see. They pray most of the day, together and individually in shifts before the Blessed Sacrament, generally waking up at 5:15 a.m. to prepare for the first daily service, going to bed after the 8 p.m. final prayers.

All the sisters have jobs. Some craft Mass cards and rosaries, the sales of which support the convent. Other sisters respond to letters and answer the phones. Some callers are lonely; others are suicidal. Just listening, the sisters say, seems to make a difference.

The sisters get one hour of free time and one hour of recreation each day. They are allowed visits from family and friends three times a year.

Sister Mary Angelica, 55, said she wants people who have lost touch with their faith to know there is always someone praying for them, “no matter what their need may be.”

The sisters follow current events, but the newspapers they receive don’t include the sports or entertainment sections.

“We try to be as simple as possible so we can focus on the Lord,” explained Mary Angelica. “We are simple in everything, even meals — though on special occasions, we have ice cream.”